We don't vote for a name on a ballot, we vote for an elector who may or not be pledged, i don't recall how pledging works legally. If kamala is disgraced/quits/gets offed by Hillary, but gets the elector, Hillary can certainly swing the elector. Or Mike. Or pencilneck Adam Schiff. Or you or me. The electors vote for the President via the state legislatures in some fashion and the states send their determination to Congress for a Jan 6 tally, except Nebraska and Maine who have split systems where the legislatures can send a split ticket.

Most elections, one party concedes before the legislatures even receive the electors, so it's mostly been a ceremonial task from the day after the general election until 2020. 2000 was determined by the courts due to hanging chad.