Interesting stuff. So the voters would basically be electing Democratic electors, nominally pledged to Carter, who would then simply go on to vote for Mondale when the electoral college met?
On Oct. 16, 2000, Missouri Governor Mel Carnahan, candidate for the US Senate, died in a plane crash. There was no time to change names on the ballot before the November election. Lt. Governor Roger Wilson became governor and promised to use his power to appoint Jeanne Carnahan (Mel's wife) to the seat if the voters elected the Late Mel Carnahan. By voting for a dead man, the voters were electing a vacant seat. The vacancy won over Assembly-Of-God Republican John Ashcroft, and Jeanne Carnahan was seated.
On the national level, if the ticket was half empty, the voters would still be electing electors of their respective parties. Different states have different levels of binding or obligation for their electors. In any case, it is up to the electors alone (subject to state law and party influence) to choose the president if the intended candidate is deceased.