All we have is what the power says. It says that a minor action can be used to sustain it, and that an attack occurs when that happens. Thus, the most direct explanation is that... you can sustain it, and when you do an attack happens, and nothing else enters the picture.
Any other interpretation involves actively changing the power. And, as written, "Sustain Minor: The blindness persists until the end of your next turn" seems a much more significant change than simply allowing it to continue operating as written. Especially since it starts to add a lot of rules complications - can you not sustain if you didn't bloody the enemy? If the enemy does, can you no longer sustain?
It also very much does not match the description of the power. I know, I know - you can't make rules based on flavor text. But in a situation like this, where wording is unclear, I'll go with an interpretation that is a perfect match for the description, vs one that is completely unrelated (and even contradictory) to it.
No, the rules say that "A power’s description indicates what happens when you sustain it or let it lapse."
Actually, that is what the Compendium says. Checking the PHB itself (page 59) makes this even clearer:
"If a power has a “Sustain” entry, you can keep that power active by taking a specified type of action (minor, move, or standard) during your turn. The “Sustain” entry tells you if a power has an effect that occurs when you take the action to sustain it."
One of the examples given even matches our situation: "Sustain Minor: When you sustain the power, you make a secondary attack."
So, you don't actually need an effect to sustain. Sustaining it simply keeps that power active. If you stop sustaining it, the power is no longer active, and can no longer be sustained. And, for emphasis, the sustain entry tells you what happens when you do.
Whereas by your argument, anything that has a sustain effect would sustain all effects of the power, rather than simply those mentioned in the sustain entry. That doesn't seem to match what the rules say, nor does it match how they have implemented allother sustainable powers.
Let's look at other PHB Sustain Powers. The vast majority of them, in the sustain line, says, "The zone persists" or "The barrier persists" or a similar line.
We do have the following three powers which, like Crown of Stars, involves sustaining a power to inflict a secondary attack, with no actual effect in play to be sustained:
[sblock]Radiant Pulse ("Sustain Minor: When you sustain this power, you can repeat the secondary attack (the primary target is the same each time).")
Note: No conditions are applied, thus demonstrating one can indeed have sustainable powers that work this way.
Curse of the Dark Delirium ("Sustain Standard: You repeat the attack against the target as long as it is within range. On a miss, you can’t sustain this power.")
Note: While the attack allows conditions inflicted by the original attack to be reapplied, they do not automatically persist. No actual effect is being sustained, aside from the ability to repeat the attack.
Doom of Delban ("Sustain Standard: You can attack the same target or switch to a new target within range. Make an attack (as above) and increase the cold damage by 1d10 each time this power hits. Each time you sustain this power, you take 2d10 damage.")
Note: Again, no conditions at hand, just the ability to make attacks.[/sblock]
On the other hand, we also have three powers that features a zone or conjuration that do not explicitly state they persist in the sustain line:
[sblock]Tendrils of Thuban ("Sustain Minor: Make a Constitution vs. Fortitude attack against all targets within the zone. On a hit, the target takes 1d10 + Constitution modifier cold damage and is immobilized (save ends).")
Flaming Sphere ("Sustain Minor: You can sustain this power until the end of the encounter. As a standard action, you can make another attack with the sphere.")
Bigby's Icy Grasp ("Sustain Minor: A target grabbed by the hand takes 1d8 + Intelligence modifier cold damage when you sustain this power. As a standard action, you can attack another target with the hand, but it must release a target it has grabbed.")[/sblock]
We also have the following that, originally, feature sustain lines without explicitly saying what effects were sustained. All of the following have, however, recieved errata to fix those issues.
[sblock]Spiritual Weapon ("Sustain Minor: When you sustain the power, repeat the attack. Your allies continue to gain combat advantage against the weapon’s target.")
Note: This has received errata that now says, "Sustain Minor: You can repeat the attack against an enemy in the weapon’s square, and the weapon persists until the end of your next turn."
Astral Storm ("Sustain Minor: When you sustain this power, make a Wisdom vs. Reflex attack against every enemy within the zone, dealing 2d10 + Wisdom modifier lightning damage if you hit and half damage if you miss.")
Note: This has received errata that now reads: "Sustain Minor: The zone persists until the end of your next turn, and you can make the secondary attack.")
Hunger of Hadar ("Sustain Minor: When you sustain the power, you make a secondary attack.")
Note: This has received errata that now says, "Sustain Minor: The zone persists until the end of your next turn, and you make a secondary attack."
Evard's Black Tentacles ("Sustain Minor: When you sustain the power, repeat the attack against any creature within the zone that is not immobilized, and deal 1d10 necrotic damage to creatures that are immobilized.")
Note: This has received errata that now says, "Sustain Minor: The zone persists, and each creature within the zone takes 10 necrotic damage."[/sblock]
Additionally, we have the following powers which previously featured weird sustains (often involving secondary attacks or effects) - and have received errata removing the sustain element entirely:
[sblock]Battle Pyres ("Sustain Standard: You can make the secondary attack in subsequent rounds as long as at least one of your primary targets is taking ongoing radiant damage.")
Note: This has received errata, removing the sustain entirely, and now reading, "Effect: Until the ongoing damage ends on every primary target, you can take a standard action on your subsequent turns to repeat the secondary attack."
Curse of the Dark Dream ("Sustain Minor: You slide the target 1 square, whether you hit or miss (save ends).")
Note: This has received errata, removing the sustain entirely, and now reading, "Effect: The target is subjected to the dark dream (save ends). Until this effect ends, you can slide the target 1 square as a minor action once per round, starting on your next turn."
Crown of Madness ("Sustain Minor: The target makes a melee basic attack against one of its adjacent allies of your choice (save ends).")
Note: This has received errata, removing the sustain entirely, and now reading, "Effect: The target is subjected to madness (save ends). Until the effect ends, you can use a minor action once per round, starting on your next turn, to cause the target to make a melee basic attack as a free action against one of its adjacent allies of your choice."
Curse of the Bloody Fangs ("Sustain Minor: The target and any of your enemies adjacent to it take 1d10 damage (save ends).")
Note: This has received errata, removing the sustain entirely, and now reading, "Effect: The target is subjected to bloody fangs (save ends). Until the effect ends, you can use a minor action once per round, starting on your next turn, to deal 1d10 damage to the target and each of your enemies adjacent to it."
Curse of the Black Frost ("Effect: If the target moves for any reason, it takes 1d8 cold damage (save ends). If the target saves, you cannot sustain this power. Sustain Minor: The target takes 2d8 cold damage.")
Note: This has received errata, removing the sustain entirely, and now reading, "Effect: The first time the target moves on each of its turns it takes 1d8 cold damage (save ends). Until the effect ends, you can use a minor action once per round, starting on your next turn, to deal 10 cold damage to the target."
Summons of Khirad ("Sustain Minor: Make a Constitution vs. Will attack against the target. On a hit, you teleport the target to an unoccupied square within 3 squares of you. On a miss, the effect ends.")
Note: This has received errata, removing the sustain entirely, and now reading, "Effect: Until the end of the encounter, once per round as a minor action, starting on your next turn, you can make a Constitution vs. Will attack against the target if it is within range but not necessarily within line of sight. On a hit, you teleport the target to an unoccupied square within 3 squares of you. On a miss, the effect ends."
Thief of Five Fates ("Sustain Minor: Make a Charisma vs. Will attack against the target. On a hit, the effect continues. On a miss, the effect ends.")
Note: This has received errata, fully overhauling the power and removing the sustain effect entirely.
Curse of the Golden Mist ("Sustain Standard: Make a Charisma vs. Will attack against the target. On a hit, the target loses its next standard action. On a miss, the power ends.")
Note: This has received errata, fully overhauling the power and removing the sustain effect entirely.
Fireswarm ("Sustain Standard: Make a Constitution vs. Fortitude attack against the target. On a hit, the target and each creature adjacent to it takes 2d10 + Constitution modifier fire and poison damage. On a miss, you deal half damage and the power ends.")
Note: This has received errata, removing the sustain entirely, and now reading, "Effect: Until the end of the encounter, you can take a standard action once per round to make a Constitution vs. Fortitude attack against the target. On a hit, the target and each creature adjacent to it take 2d10 + Constitution modifier fire and poison damage. On a miss, you deal half damage, and the power ends."
Thirsting Maw ("Sustain Minor: The target takes 2d8 damage (save ends). Each time the target takes this damage, you regain hit points equal to half the damage.")
Note: This has received errata, removing the sustain entirely, and now reading, "Effect: The target is subjected to the maw (save ends). Until the effect ends, starting on your next turn you can use a minor action once per round to deal 10 damage to the target, and you regain hit points equal to half that damage."
Delusions of Loyalty ("Sustain Minor: When you sustain this power, you can repeat the attack against the target. If you miss, you can no longer sustain the power.")
Note: This has received errata, fully overhauling the power and removing the sustain effect entirely.[/sblock]
Finally, there are a handful of powers whose sustain effect originally said, "The effect continues", and now explicitly state, "The effect continues until the end of your next turn."
Conclusion:
So, what does this tell us? Well, we have 'proof' in both corners - we have at least two powers that flat-out have no conditions even capable of being persisted by a sustain effect. I'd say that stands are pretty conclusive evidence that Crown of Stars can indeed keep operating even if it doesn't persist the blinding effect.
We also have a number of powers who worked similarly, and received errata to remove the 'sustain' element entirely - such as Summons of Khirad and Firestorm. Perhaps, in an ideal world, Crown of Stars (and the others like it) would receive errata to make them match that approach.
On the other hand, we do have several powers that do not explicitly state, in their sustain line, that they cause the original zone or conjuration to persist. Now, that might serve as evidence that the blindness could indeed continue... however, I see a few things worth noting.
First of all, there is certainly a clear effort made in many other powers, in the errata, to ensure that they do make clear what is persisting due to the sustain (and for how long).
Secondly, of the powers that still don't make it clear, both Flaming Sphere and Bigby's Icy Grasp) don't include any initial durations, either, so clearly have some issues already. The sustain lines also don't feature a description of how long the sustain extends the power, which I see as further evidence that these are probably not powers we should look to for setting precedent.
Tendrils of Thuban seems to be the only power where the sustain line makes no reference at all to making the intended target persist, and given how every other power like that was fixed by errata, I'm inclined to chalk that up as an oversight, not as some hidden insight into the rules.
