They might also start using a different word: “sedevacatism”. The empty chair. It’s a Catholic thing — some (heretical) Catholics believe that the Pope has not been a true Pope since the death of Pius XII in 1958.
If Hillary is replaced with (say) Joe Biden, would the voters consider him a “real” nominee? They didn’t pick him.
Why Biden? Sanders did quite well against a system that was rigged against him. Had Biden run he’d have had zero votes against Hillary and Bernie? If I were a Bernie supporter I’d be livid if that ever happened.