I predict they will litigate it all the way to the supreme court.
So do I, and will be more than one lawsuit. America probably won't know who is their next President until sometime in December. All lawsuits will be expedited up the judicial system to the USSC. Remember, Bush vs Gore. That was a simple decision because Florida was trying to change their election laws mid-stream. The coming suits will be about voter fraud and about voters not receiving their absentee ballots.
That is why I and the wife are going to drop off our mail-in ballots at an official polling location on 11/3. I don't trust the USPS anymore. With 6 hundred thousand employees, any sorter or delivery person can just trash ballots from Republican zip codes.
Once we overcome Corvid, I believe that other than out country military and truly infirmed should have to vote in person at official polling places.