Constitution prohibits re vote
The constitution does, but if the state legislature ordered another vote in order for the votes to be counted I believe it would be constitutional.
It is the only remedy. There is no other way to accept the vote and the legislature would not want to unilaterally decide the election. Call it a safety valve for politicians.
After all, this is pretty high stakes and people will not trust the result otherwise. Why would Biden be afraid of this? He won, right?