I wonder if in order to defeat the Night King, Jon will have to kill Bran
I believe this is what will happen. Bran will probably try to warg into the dude that became the night king to stop the COTF from transitioning him but will be too late and get locked into him in permanent status. Blood Raven warned him of trying to mess with the past. Once Bran is locked in, that is where i believe Jon will have to sacrifice him to end the threat.