What happens if Avatar: Fire and Ash doesn’t make enough profit to convince Disney to bankroll Avatar 4 and 5? Creator James Cameron has said he’s ready to walk away from the franchise, adding he’ll write a book to resolve the one thread Avatar 3 leaves open.
If they do make it, then they get to feature the not airbenders for Avatar 4.
And then the Not Avatar will come to save the world in Avatar 5.