As noted in an earlier post, there are plausible scenarios under which next month’s election could result in a 269–269 electoral vote tie, which would send the presidential election over to the House of Representatives. Such an outcome would favor Romney over President Obama, according to an analysis by the Washington Examiner.
But in such a case, it would fall on the Senate to choose the vice president, with each Senator getting a vote. Given that it’s quite possible (arguably likely) that Democrats will retain control of the Senate, it means that they could vote for Biden to remain on as VP, even if the House elects Romney as president.
In theory, if the election outcome is a 50-50 Senate, Biden could be the tie-breaking vote for himself.