If he drops out for any reason he will blame America and say that he can't count on a fair election, whether in the primary or the general.
The thing is when it comes down to it will GOP voters really pick DeSantis over him? I don't know.
Depends on how tired of losing they get. We'll see what happens in Georgia tomorrow. If Warnock wins then Trump will likely take the blame again for that one, but if Walker wins then that's a big wild card.
What about a Trump/DeSantis ticket?
Trump doesn't like DeSantis and won't pick him. Trump is too insane at this point for anyone to be willing to vote for him because they like his VP. Though interestingly enough his VP is more important this time around since, if he wins, Trump is very likely to die in office. I doubt a man north of 350 pounds will live to be older than 82 when he already clearly fails to cope with the stress of the presidency.