I'm fairly sure Rich just forgot or took narrative license with Xykon's paralysis making O-Chul paralyzed in his current stance, rather than falling paralyzed to the ground as though he was dead. Given that, I'd say that O-Chul hasn't shown the XX eyes because his body is still paralyzed, even though he's probably dead now from being hurled that far by the explosion (through walls/ceilings and such no less).
I'm fairly sure O-Chul is dead, he's left in that pose simply for humor's sake and probably for a bit more dramatic tension.
Miko took O-Chul's sword or one of the other Sapphire Guards' swords, to smash the Sapphire Gate.
Miko could not be at full health. The laws of Azure City may've required that she be healed a bit to ensure surviving to her day of trial and execution for high treason. But she would not have been fully healed after her tough battles with Roy and Hinjo after slaying Lord Shojo. And there hasn't been enough time yet for her to naturally heal much from that battle.
I'm fairly sure Miko is either dead (explosion, smashing into walls, getting hurled a great distance), or saved by the Snarl for destroying one of the Gates that have been sealing it and restraining its ability (two are gone now, out of a handful, so a decent bit of the Snarl's power is probably able to reach out of its prison now).
Slow Fall requires using a wall to skid down and slow the fall. It will not save Miko. And she only has a few levels of Monk, at most, before her zealous focus on Paladinship. She has no Improved Evasion, nor Wholeness of Body or anything else significantly helpful to her survival at this point.
The Snarl may've reached out with its newly-released bit of power to save Miko, expecting that since she destroyed part of its prison, she may destroy the other parts. Miko of course will believe that this truly is the will of the 12 Gods, that she destroy the gates so Xykon and others cannot use their power. And she would inadvertently release the Snarl, which would of course ensure she doesn't perish from the destruction of each Gate she smashes.
Miko has most assuredly NOT been redeemed by destroying the Gate. It doesn't matter that Xykon and Redcloak are escaping rather than taking the Gate. The hobgoblins who survive the explosion (likely too far from it compared to others) will continue their assault. Xykon doesn't care about them anyway, and he can always gather another force with Redcloak's help, probably. Redcloak's in no position to demand that Xykon call for the hobgoblins to retreat and follow them, and he might not think of it right away.
Those Azurites who couldn't fit on the ships, especially considering that the rich folks took off with nearly all the ships while leaving much of the citizenry behind, may die from the explosion or from any hobgoblins who survived it.
Miko ignored the fact that Xykon and Redcloak were on the ground, the founder of Azure City hovering over them and ready to strike the final blows. She destroyed the Gate when clearly it was no longer necessary, and when she had known (IIRC) that the city was founded in the first place to guard the Sapphire Gate.
If Miko or the OOtS had shown Xykon's and Redcloak's inanimate corpses to the hobgoblin force, the hobgoblins may've lost their morale and fled, or something.
She is too absorbed in her own ego and feelings of 'specialness' to be a paladin anymore. She still fails to see that she was wrong to cut down Lord Shojo and whatnot. She won't become a Blackguard unless she takes to serving evil powers, which she will not because Miko still steadfastly believes she is the chosen of the 12 Gods.
No, if Miko somehow survives this, she will just be advancing as a Fighter or Rogue for awhile. Maybe some Servant of the Snarl custom prestige class though, unwittingly.