Avengers 4: Every Character Confirmed So Far
5. Gamora
Confirmed By: Zoe Saldana And The Avengers Facebook
Despite being dead at the end of Infinity War, Saldana herself confirmed she's back as Thanos' disgruntled adoptive daughter in the sequel to the BBC, and then appeared as the lead in the Hurricane Harvey video posted to Facebook by the main Avengers account. She was in costume on the set - it doesn't really get much more firm than that.
Saldana will also presumably return for the Guardians threequel - particularly as there's more to tell in her story with Star-Lord.
In short, she has to come back, really.