If worse come to worse then conservative controlled states need to remove the democrat candidate from the ballot.
It would come to that, and the situation would put our national ass in a sling. Pro-Trump people would only count states which put Trump on the ballot, and the Bidenistas would only count states with Joe on the ballot. In effect it would be two distinct elections (with some overlap), and neither election result would be truly legitmate. Whichever camp tried to enforce their version of the election outcome would probably faced armed resistance from the other camp.
At that point Constitutional government would have failed and only the military could sort things out.