There are crazier things out there.
But none of us really know - if Trump has *really* got the fix in (not just redistricting and postal ballots, but right-at-the-heart Kremlin-style lying), he'll stay on till the end, and it will all just get worse and worse.
But I can't see Thiel et al standing for it, after the money they've put in for Vance. Putting Vance to a public vote for the first time in 2028 would be too risky because, as you say, he's no cult leader - so they need him to become president for a couple of years without the need/potential downfall of an election, and then promote him from there.
After Trump, putting my cat in charge would restore sanity, so 2028 would be Vance's to lose. The big boys get to keep all of their money, the racists are kept happy and the uncritical masses see some improvements at the petrol pump and supermarkets. Why vote for change after that?