I could see it playing out like this:
Cardale is named the starter, Braxton switches to HB/WR like a Denard Robinson or Randall Cobb, and fills in as a backup QB if needed. JT redshirts.
After a few days celebrating the 2016 championship win, Cardale declares early for the draft. He and Braxton are gone, and JT is the starter for 2-3 more years.