Peter being friends with Future Hiro has nothing to do with Peter exploding. Don't assume that Peter is going to do it on purpose - it's possible he couldn't control it.
It's a definite that Peter survives, and he has a scar. It might have something to do with the exploding episode.
As for Sylar being able to use his powers in the cell, it might be possible that he used his initial sense of "being able to see what makes things tick" - in this case, the cell - and changed his brain once again to bypass it. It should also be interesting to note that Eden's power of persuasion no longer worked on Sylar. He probably fixed his brain to become immune to that as well.
If that's the case, then Sylar is indeed someone very powerful and dangerous.
It's a definite that Peter survives, and he has a scar. It might have something to do with the exploding episode.
As for Sylar being able to use his powers in the cell, it might be possible that he used his initial sense of "being able to see what makes things tick" - in this case, the cell - and changed his brain once again to bypass it. It should also be interesting to note that Eden's power of persuasion no longer worked on Sylar. He probably fixed his brain to become immune to that as well.
If that's the case, then Sylar is indeed someone very powerful and dangerous.