Originally Posted by
IrishDevil
1) I think you are correct, we do not see 2014 Gamora during the final parts of the battle or its aftermath, but it is implied that she survived (Quill is running a search for her onboard ship when we see the guardians depart). Perhaps Tony's snap eliminated Thanos and those serving him, and Gamora's shift in allegiance protected her from getting dusted?
2) Nebula knows that Thanos took Gamora with him to retrieve the soul stone and returned with the soul stone, but without Gamora - she says as much when Thanos is restrained on Titan, which sets Quill off, makes him temporarily an idiot, and prevents our heroes from taking the gauntlet from Thanos. I would be interested in watching Endgame again to see whether we are given any indication that Nebula, Hawkeye, or Black Widow understands what must happen to retrieve the soul stone in 2014. Nebula ought to have, but I'm not sure she would have felt inclined to share that with anyone.
3) They (Stark? Hulk?) expressly stated in Endgame that Back to the Future logic does not apply in the MCU, even laughing at Scott Lang when he brought it up.
In Back to the Future, you can only travel back and forth along a single timeline, so if you create a branch in the timeline by changing the past, you have to correct that branch in the past in order to return to your original future. This would have posed a huge problem for Endgame, where our heroes had to travel into the past, change it by taking the infinity stones, then return to their original timeline's 2023.
I think this is how it works in the MCU: as the Ancient One explains it to Hulk when he retrieves the time stone in 2012, changing the past creates a branch in the timeline resulting in an alternate reality, another segment of the multiverse. The original timeline still exists, which eliminates the Back the Future II problem, but there is also an alternate timeline branching from the change in the past that runs parallel to the original timeline. Time travel in the MCU, therefore, is not just traveling along a timeline, but jumping from timeline to timeline. Into the Spiderverse plays with this device to bring in multiple universes' versions of spiderman/pig/gwen, and the current season of Agents of Shield and Spiderman: Far From Home seem to employ it, as well. I will be curious to see how the next phase of the MCU deals with, uses, or distances itself from the multiverse.