lawfag here
having dug on this once again its clear as MUD
there is a patchwork of laws and practices and of course the constitution - none of which answer this definitively (if at all)
so many opinions but the only opinion that counts is SCOTUS
my guess is chaos and litigation no matter what assuming election is held as scheduled
i also believe there is POTUS ER power by law (cant point to it sorry but im sure its there just too many to know all) which will justify whatever he decides to do -
delay or stay in office until SCOTUS rules on one or more cases
that will be before 1/21 however so no crisis IMO
also POTUS has full exec power over post office and other agencies that are critical to election so that figures in too
i trust all is planned with all contingencies considered