The problem DeSantis has if he actually beats Trump in a contentious Primary is similar to the problem that McCain had, which was that a HUGE number of Republican voters will not vote for anyone but Trump in November (probably 20 million or so). In McCain’s case, he had to pick Palin to get some of the base back. For DeSantis, I cannot see what option(s) he might have and without those voters, the Democrats won’t even have to bother cheating. Nor will those Republican voters ever forgive DeSantis.
So, based on that, I don’t see DeSantis running, particularly given his (young) age.
Trump has the same problem in reverse
If Trump is not the nominee, his loyal supporters will certainly get behind DeSantis. Versis Biden or one of the other idiots - of course.