My guess is that the DNC will pull a switcheroo and put in Biden, just as she is about to be indicted. Biden will have missed the primaries and debates, where he would have been doomed every time he opened his mouth. With limited exposure and a very, very friendly press, his idiocy can be masked enough, they think, to get elected. They will tell Hillary and Bernie, about 24 hours before it happens.
You may have something there.