The U.S. Postal Service handles 472 million pieces of mail each day. If 100 million people decide to vote by mail then, taking account of the initial request for an absentee ballot and the return of the absentee ballot to the voter and the return of the completed ballot to the state registrar, absentee voting will add 300 million pieces of mail over roughly 6 weeks. In other words, this will add a burden of additional mail equal to roughly 1 1/2% during that time.
The Postal Workers Union has just endorsed the Biden ticket.
All the fuss about postal delays is likely to frontload the mail-in ballot burden, so that any additional time in delivering the final ballots will probably not make too much difference.
I suspect we are going to be okay.