Avengers 4: Predicting The Fate Of Every Avenger
19. Mantis
Current Status: Dusted
Her Avengers 4 Fate: Mantis was a lot more useful against Thanos than anyone anticipated. She was able to dull his mind and knock him unconscious, and had Star-Lord not lost his temper, her power would have helped the team snatch the Infinity Gauntlet.
Considering she was only just introduced into the MCU, she won't be killed off in Avengers 4, but at the same time, she's the very definition of a B-hero. If she does have a huge, character-altering arc, that will play out in Guardians Vol. 3, not in a team-up movie that has dozens of things to do already.
Mantis' powers are too cool and too useful to go unused though, so expect to see them put to good use once again when she returns from her current dusty form.