I think it was probably a Steve/Tony fic. The Avengers are under some sort of attack, and Tony ends up pretending to be dead as part of a master plan to defeat their enemies. The other Avengers don't know about his plan, though, and mourn him as dead. I think there is a reunion scene when he comes back, showing all of their reactions.
I know this is super vague, but I can't remember any other details really! Any help very much appreciated! :)