If Biden or the Democratic party really cared about the country they'd pick a new candidate. It wouldn't take much to beat Trump and if Trump is such a threat to democracy then why run the worst presidential candidate of my lifetime? Why run the only candidate that Trump could possibly beat?
I think if they swapped that person would certainly lose, mostly because there just isnt another person that is both palatable to elites and popular (except maybe Michelle Obama?) to have people actually vote for them.