The story was set at the start of the end of the world, or almost, and everyone else is panicking. Sylar goes to find Mohinder and they watch a documentary about birds, and there is sex. It's a sad fic, mainly because Sylar will be revived (because of his powers) and Mohinder won't, so the whole 'enemy' aspects of their relationship don't matter anymore.
Lots of thanks if anyone can help me find this story again. <3