Peter stood there so he could try to absorb Sylar's powers. Right as Sylar let the glass go the blackboard came flying at him from behind. Maybe Peter knew that would knock him out and would allow Mohinder to get out of there. Peter believed, before that, that he could heal ala Claire, but did not know that a piece of glass to the head inhibits the healing. Peter stood there to help Mohinder and heal himself.
I think Mohinder rammed the blackboard into Sylar.Did Mohinder bring a dead Peter to his mothers in a taxi? How weird is that?
Sylar had time to walk to Peter and stand over him, then the blackboard smashed into him. It was definetly Mohinder (or maybe the smoke monster

)In the final scene with current Hiro and future Hiro, the timeline only shows save Claire, bomb goes off, and something about Nathan being a rock in a bad time. I think the shot of Sylar on TV was in the previews.When Hiro and Ando are talking ont he roof, Hiro says something along the lines of "Don't you remember, they caught brain man so maybe Issac is still alive" What was he referring to?? Is he assuming that the past will change?? Why did he think they caught Sylar??Didn't Doc Brown explain to Marty that you can't interact with your future self without causing a rip in the space-time-continuum??