Thanks all for the replies!
This is just what I was thinking - you get to make the check, but it's only going to be relevant if you have cover or concealment (but not superior/total, due to Cunning Sneak), unless there are other powers/effects in play.
Superior/total is irrelevent. You've -made- the check, so you only need normal to maintain it. What you need superior/total for is when you make a steath check as part of a normal action. Outside that case, you do not.
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This is pretty cut and dried (and thus I like it) - but where is it from? I cannot find that exact phrase in the rules. Also, it seems to contradict this part of the stealth rules:
If you do not lose hidden status until the end of the action, you would not need to "retain the benefits".
Is there a meaningful difference between being hidden until the end of the action and having all the benefits of being hidden until the end of the action?
The difference, in practical terms, isn't important enough to worry about. There MIGHT be a corner case where you have a power that kicks in when you become unhidden that also happens to be a free action... but other than that singular instance, it doesn't matter a bit.
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(4) If my rogue is hidden, makes an attack that with an after-the-attack effect that includes "make a stealth check to become hidden", and successfully makes his stealth check - was he ever NOT hidden at any point in there?
Yes.
Technically, as soon as he makes the attack, however that doesn't affect him mechanically until after the -action- is complete.
However:
After the attack, the stealth roll is irrelevant; he is not hidden, unless the power somehow allows you to make a check to -remain- hidden.
Not Remaining Hidden: If you take an action that causes you not to remain hidden, you retain the benefits of being hidden until you resolve the action.
You can’t become hidden again as part of that same action.
If hidden status is retained until end of action, then he never lost hidden status - but this just doesn't quite feel right (this could easily be a melee attack as well as a ranged attack).
Well, it doesn't matter when he loses it. He still has the full benefit of being hidden (including enemies not being able to see him, important for opportunity attacks) until after the -action- is complete.
However, it shouldn't be a problem, after the action is complete, he doesn't get to make his stealth roll because one can not become unhidden and become hidden in the same action.