If he lost the EC, of course I would not support his remaining. Even if he lost due to Faithless Electors, he would have lost and would have to leave. Of course, the worst outcome I see if Trump lost is Trump being a Sore Loser in the style of Stacey Abrams mold and some legal challenges, but he won't hunker down.
If he wins the EC and then faithless electors throw it to the opponent, that is the kind of situation where Trump doesn't leave and his base supports him. I don't want to think about how that could end up. Best case scenario, SCOTUS does a Bush v Gore, giving Trump the win, to avert massive unrest.