I think Sexton will start at the 1 for as long as he's on the team. If Collier has to beat out Sexton, that's going to take a while. If Sexton gets traded, that opens the door for Collier to start and share on-ball reps with Keyonte. This assumes that Clarkson will also be traded, resulting in our starting backcourt being Collier and Keyonte.
Collier needs to prove a few things: a) that he can defend his position and preferably up a position, b) that he can shoot efficiently, and c) that he has an impact when he's off the ball.
If the Jazz are able to draft either Dylan Harper or Nolan Traore next summer, then that guy would be expected to become the starter by half way through their rookie season. Collier would be a backup or would be moved, imo.