We’ve speculated about Killmonger’s death being retconned through whatever time-travel/Quantum Realm shenanigans take place in Avengers: Endgame.
The snapped heroes are certainly coming back, so it wouldn’t be impossible.
These are comic book movies after all.
If Courtney B. Vance really let a spoiler slip here, there are some huge questions as to how exactly N’Jadaka will be in this movie after he willingly chose death over bondage at the end of the first film.