I don’t know if the DNC can swap Biden in for H. Maybe the lawyers can comment but I would think that since the ballots have been printed up there is a date beyond which the DNC is stuck with her. I suspect the Wikileaks people know this and so the crescendo of crap they are dumping on her is timed to accelerando (no mixed metaphors) just as that date passes.
From what I understand the electors are based on the ticket. The DNC would wait until the last possible moment so as to not affect turnout.