Extraordinarily unlikely, except in the fantasies of some Russians. If Trump wins, we wouldn’t get violent until he actually tried to suspend the Constitution, that would be the most likely instigating event. Not people voting for him and him winning, sadly, fair and square by the laws of our land.
The die-hard Trump supporters are too few in number to do anything if Biden wins. Civil war-wise anyway, they could probably manage a bunch of terrorist attacks if they were angry enough.