I would not be surprised if he leaves but i Don't think he will. If he does,it will go down as one of the most odd coaching situations in BYU history. All that potential, all that success, all that unfulfilled, retiring so young. Unless, he goes for some really big bucks in a big program for a few mostly intolerable years, that has far fewer opportunities to teach character and religion at the level that Bronco clearly feels is a priority; and where fans will be just as passionate and/or rabid and even more critical when football is fifth.
I wouldn't blame him if he wants to spend more time with his boys. I would totally get that and say Heaven bless him.
Otherwise, I suspect he will sign a series of one-year with option to renew type of contracts. His word is important to him, but so is his freedom. He would not play BYU as other coaches have played their universities and leave earlier than his commitment to stay,