Considering anyone who watched Avatar seemingly watched Neytiri kill Quaritch, Avatar 2 will have to explain his return, which could be done in any number of ways. For his part, Stephen Lang told The National it felt satisfying to know James Cameron wanted him to come back that much:
Article source: https://www.cinemablend.com/news/2491582/avatar-villain-stephen-lang-opens-up-on-quaritch-surprise-return-avatar-2-much-broader-canvas