Hiro time traveled from the future and retrieved the film, but used a Kevlar vest to protect him from Samuel's attack so he only seemed dead before trapping him in a mental institution so he disappeared as if he was dead.
Hiro time traveled from the present and retrieved the film, but used a Kevlar vest to protect him from Samuel's attack, so he only seemed dead. Later he trapped Mohinder in a mental institution so he stayed disappeared as if he was dead.