If Trump loses, there may be no GOP left for them.
If Trump starts a new party, and the size of the GOP shrinks, their only chance to stay relevant would be to join the Rats.
If Trump loses you are correct the base will desert them in ways they haven’t even begin to imagine. They will lose the congress and then start losing in state and local elections on a massive scale. My Dad, a conservative before Goldwater was ever a candidate made the comment to me this week after listening to the all the idiot so-called “conservatives and Republicans” trashing Trump that if he loses he is done with the Republicans on every level and won’t vote for another of these traitors. The GOPE are the biggest fools I have seen in many a year.
But based on their behavior the last twenty-five years they are too stupid to see the suicide they are committing and the loses that will follow their treachery. Look out for a third party formation and eventually the GOP folding into the Democrat party or blowing away like dust in the wind.