I'm fairly certain that this has happened before, at least the senatorial level. There is definitely a mechanism in place to deal with such an occasion. Probably something like elect the ticket, VP takes office. Most recent case I can think of that is similar would be FDR/Truman in 1944. Don't worry about it though. We'll still get taxed and screwed and life will go on.
How ironic, post 666 and it's on politics...... :-\"