Dead by Election Day
What happens if a presidential candidate passes away at the last second?
http://www.slate.com/articles/news_and_politics/explainer/2008/09/dead_by_election_day.html
what would happen if one of the presidential candidates were to die or become otherwise incapacitated before Election Day: Would Palin or Biden assume the nomination?
Not necessarily. Each party has its own protocol for this scenario, but in neither case does the running mate automatically take over the ticket.
If John McCain were to die before the election, the rules of the Republican Party authorize the Republican National Committee to fill the vacancy, either by reconvening a national convention or by having RNC state representatives vote.
The new nominee must receive a majority vote to officially become the party candidate.
If Barack Obama were to die before the election, the Democratic Party’s charter and bylaws state that responsibility for filling that vacancy would fall to the Democratic National Committee, but the rules do not specify how exactly the DNC would go about doing that.
(Congress could also pass a special statute and push back Election Day, giving the dead candidate’s party time to regroup.)
What if the candidate dies after the election but before the inauguration on Jan. 20? The 20th Amendment states that if the president-elect dies before beginning his term, then the vice president-elect assumes his or her spot.
However, the point at which a candidate officially becomes “president-elect” is debatable. He or she definitely assumes the title after Jan. 6, when a joint session of Congress officially counts the Electoral College votes and declares a winner.
But the shift could be said to occur immediately after the Electoral College vote.
They would go Biden -Kaine