I think it's Peter. I don't know how the whole "Save the Cheerleader" thing altered the timeline, but remember when Hiro teleported to Issac's apartment before the explosion and saw a newspaper that said Nathan wins the election by a landslide? I'm thinking that Peter dies and Nathan, being the selfish ass we have seen, uses it and his wife's paralysis to his advantage to gain the sympathy vote.
I don't think it's Peter. When Hiro teleported from the future to deliver a message to Peter he told him that he looks different without his scar, which implies that Peter is still around in the future.
But Hiro came back to tell Peter to save the cheerleader, which may mean that in the future Hiro came from she died, so that would change things quite a bit...