Avengers: Endgame simply changed all the pending sequels of the Marvel Cinematic Universe. For example, Guardians of the Galaxy Vol. 3 will have to include Thor by force and have a completely different Gamora than we know.
This last case is somewhat special, since Thanos sacrificed his daughter to obtain the Soul Stone in Infinity War. While in Endgame, it was revealed that a version of the character's past would time travel five years alongside his father.
For now, it is unknown if actress Zoe Saldana will return to the Marvel Cinematic Universe, but she will practically have to take on a completely different role. Gamora is still in the process of switching to the good side.
James Cameron did a Q&A on Instagram where he revealed that he already knew the character's fate. He commented that he doesn't feel sad about the decision to change the character.
"Simply put, everything was discussed in advance," the filmmaker commented on the events in Avengers: Endgame and Infinity War.
The actress simply responded that "it depends" on the writers if she returns to the MCU or at least in Guardians of the Galaxy Vol. 3.