So, there are theories going around about how the characters that were ashed in the snap will return. Time Travel. But what about those that have been sacrificed to the infinity stones themselves? What about Gamora?
Spoilers for those who haven't seen Avengers: Infinity War: It is known that Gamora is Thanos's sacrifice to gain the Soul Stone. In the comics, the Infinity Stone's power is over life and death, and it works by capturing a person's essence and storing it in the Soul World, a plane that exists in the stone itself. Which is outside of time and space as we know it apparently. So if the remaining Avengers were to travel back in time. Gamora would still be trapped wherever the soul stone put her.
Apparently, the owner of the Soul Stone is also able to release any souls captured within it and enter the Soul World at will. If the MCU follows the comics, that explains the dream-like scene at the end of Infinity War when Thanos speaks to a younger version of Gamora after he's wiped out half the universe's existence. This also means that Gamora's soul is still around and thus can be rescued!
We have to say that Thanos doesn't seem like the type of guy who would sacrifice himself to bring Gamora back no matter how much he claims he loves her. But you never know, Thanos is a character in the MCU that is so powerful, that he cannot be defeated and thus his only weakness is his need to be defeated. You heard that right, Thanos' weakness is his need to be defeated, so Thanos sacrificing himself for his adopted daughter doesn't seem such a stretch.