Here's what I don't get . . .at some point the Nuclear Man's power will be absorbed. By whom remains to be seen. Regardless, I would think that if Sylar or Peter blew up NYC, then one of them should officially be dead! But, in the 5 year future, neither of them are. So, based on THAT timeline, it doesn't make sense that either of them did, and still survive.
Now . . .assuming Peter did, because he'd absorbed Claire's power to handle regeneration, but I don't think he'd know to switch that power on and off in a jiffy! The only possible reason is if Sylar persuaded Nuclear Man to blow up, but we all know Sylar never got HRG's assistant's brain, and besides, Sylar would need to be far off in a distance to handle a nuclear blast because either way he never got to Claire.
Brain . . . .hurts.