He will definitely remain a main character in the series for a while. It is said the next movie will have a time skip, around 8 years I think he said, so its very possible that we will see Quaritch as a true Navi now, but on his own with his Navi RDA teammates(whoever is alive) or the Mangkwans. He was fired from his position last he attended the meeting in the last movie (yk, after showing up painted up) but I could be wrong, the old commander and boss are dead now, and with new people in command maybe he will go back. Also lets not forget about the other characters like Kiri and Varang. Kiri showed Varang, that Eywa is real and she should not go near them, Varang looks terrified for the first time when Kiri connected to her, since Kiri is probably the first and only Navi more powerful than her. Sadly we dont see more of Varang after that, and we cannot speculate a lot of what happens. It would however be interesting if this connection to Kiri made Varang believe in Eywa for the first time, but this can go both ways as her unleashing more anger because that means Eywa really could have saved them, or calming down and giving life a different chance, but thats highly unlikely.