Whether he leaves or stays I doubt it has little to do with his retired pay. As others have said, he's already vested, but he can't start collecting it anytime soon.
And as I said before, state retired pay increases much quicker as your number of years in the system increases. Moving to another state starts him over. Collecting retired pay from 2 states, each with 10 years of service, wouldn't come close to equaling the amount from 1 state with 20 years of service.
But if he comes to UT, I would assume it would be for a lot higher salary, which would offset the retired pay.