It depends on what Kalani wants to optimize on... if he wants to optimize on money, then eventually he'll be gone. However, it's highly unlikely that he will be a household name at UW. They're a reeling program and he can't tout the religious components in quite the same way that fits in so well with his mantra/persona. There is a good chance he'd be out of the program within 5 years.
That being said, I think BYU needs to do the right thing and pay him so that he's not having to decide between a huge discount to coach at the school he loves. I think it's worth it for the church and BYU to recognize the amazingly positive missionary tool BYU can be. The Cormani Mclain recruiting trip is a perfect example. By all accounts, BYU is growing in popularity in Florida — a place where I doubt there are too many members of the church. It's a way to normalize members of the church, and having successful sports programs goes a long way in connecting with people that would otherwise not have any connection to the church.