2028 is five years away. A lifetime and a half in politics. Impossible to predict what would happen then.
If Trump is nominated with DeSantis’ blessings, and wins, DeSantis will be nominated with Trump’s blessings in 2028. It’s then his contest to win, and if both houses and the WH are united in the MAGA agenda and implement it, it’ll be a surefire win for DeSantis. It’s impossible to predict what will happen, yes, but it is possible to predict the consequences of present actions.