It's generally a bad idea for anyone, a coach, or an AD, to guarantee they will NEVER leave or that the coach is there for LIFE. For multiple reasons.
1. It hurts your ability to negotiate, both ways. For things like assistant salaries, facilities upgrades... I know JP is actually pretty good about doing these things for CMC so far, but in general it's not a good tactic. If JP guaranteed he'd never fire CMC he'd be pretty obligated to give him whatever he wanted and any pressure from donors would be harder to handle. I don't see those things happened at ISU right now or any time soon, but in general not a good idea.
2. Things change. CMC seems to have a great relationship with JP, but what if JP retired or got a ridiculous amount of money to go to Wisconsins or something. CMC saying he's here forever might come back to bite him if the new AD ***** things up. Other factors can affect your willingness to stay even if you love it here now.
3. The curious case of Paul Rhoads. He looked like he was taking ISU to the levels CMC has actually taken them so far, JP gave him a 10 year contract, then the bottom fell out. I don't think CMC is going to collapse, but the AD has to make smart decisions in general.