James Cameron is a very strong perfectionist. If he doesn't believe a scene is not done properly, he will redo it until it's done the way HE feels it should be done. That's why I like him, because true artists keep their project alive, even if it means having to reshoot almost an entire movie.
Avatar Sequel Release Dates Delayed Until 2020 -- James Cameron and his team have announced a new launch platform for all four Avatar sequels with the first arriving in 2020. -- http://movieweb.com/avatar-2-sequels-new-release-dates/