keep him.
People here can poo-poo the idea of a P4 coordinator taking a G5 head coaching job but it happens all the time, Hill took the Weber HC job (which is a much bigger step down than G5 USU) after being the DBs coach and ST coordinator at P12 Utah, and USU will be willing to pay him more than he’s currently making.
The allure of a HC job after running his own program for almost a decade will be strong and BYU will need to be willing to pay up! That’s all I’m saying.