I don't think the snappening is final. Not so sure about the rest, although the deaths of Loki and Gamora are a bit questionable. I wouldn't count on Gamora coming back though. There is definitely photo evidence of Tony time travelling back, presumably to the time of the first Avengers movie. Question remains, how (much) is he going to change and when he is going to effect that change. If he changes the timeline in the mentioned point within the past, then Age of Ultron won't have happened, which will perhaps revive Hydra to its former glory, and whatever will become of Civil War. If he does it, then it will be the most massive fuck-up in MCU history. I also don't think that it will happen this way, as Tony is smart enough not to change the timeline to such an extent. It will be more like a surgical operation; however, I expect it will still have unforeseen consequences. I also wonder if Tony is going to notice that Stephen's final words are a hint, although I guess that the famous last words were more of a fan service than intended for the characters. That's debateable, though.