I think Nathan died in the blast, and he is good as dead.
The result of the nuclear blast ripped Peter's body in half, resulting in the other half reconstructing itself into a clone of Peter. The "Lizards" episode, especially the part where Claire cuts off her pinky toe, confirms this. Peter, wanting to have the opportunity to lay low for a while, takes on his brother's identity. To give his clone his own identity, he takes the Peter clone, stuffs him away and gives him every shred of documentation necessary to give it a fresh start as Peter Petrelli. This explains why the clone doesn't know who he is, his first memory being wakened by the thugs, and "Nathan" being given a guilty look by his reflection in the mirror at the bar. This also explains Nathan's cold attitude toward his mother.
Both Peters obviously have the new "alter ego/superhuman" power from Nikki.
What do you think?
I know this takes the story for an interesting twist, but Nathan Petrelli has no reason to stuff Peter in a shipping crate. Peter Petrelli does have a reason to stuff away a copy of himself, and open the possibility of trumping Sylar.
