If they offer he will go. BYU could match any compensation offer but they can't give him the one thing he wants, a HC gig at a D1 school. Jay also wanted to go to USU when they hired Blake Anderson.
As for B12 vs P12, think about this, Boise is currently projected to get a bye in the CFB playoff - the B12 isn't. It will be easier to be the best conference champion and best G5 school than it will be to win the B12. Jay could easily get their program in contention and into the playoffs easier than a B12 school.
If they offer, he will go. The question is can the Cougs find a replacement that will keep our defense elite?