My best guess is a majority of them will end up voting for Trump, but not nearly all of them. I suspect he gets something like 58% of the vote statewide.
He will get 60% easily in Utah in 2020.
His approval rating in the state suggests that is not as easy as you think.
Disapproval doesn't mean they won't vote for him. The democrats leftward movement is gonna consolidate the right and right leaners. I don't think third party vote will be very high at all in 2020.
I mean feel free to look up previous presidents' approval/disapproval ratings during re-election campaigns. It's not too common to find examples where they drastically overperform their approval, and if anything it is probably becoming less common over time.