I'm happy with what you are saying -- but it is not the only interpretation of this. I just mentioned the difference in my mind between potential future and alternate timeline--and to my memory no where in the film does it specifically say alternate timelines are created when you travel to the past except when the Ancient One discusses removing the stones. I would be happy to concede the argument if somebody can find dialogue that says otherwise. As for the events that are changed--they are changed in timelines that have already been affected by the Avengers taking the stones thus when the stones are returned those timelines collapse as if they had never existed. Gamora seems to be some kind of time remnant from a timeline that no longer exists.