I’m not saying he’d let it happen, but this is one scenario where the constitution is perfectly clear and it’s within the states’ authority. They could even ignore the SCOTUS if they wanted, though I think even the SCOTUS would struggle to justify stopping an election.

Meh, just hold one without him. Get an electoral college quorum and move the new guy in because it’s 100% state driven and he can’t change the constitution. Like an old time papacy schism, let God sort it out.