If Romney repeats the electoral map of 2004, except for losing New Mexico, he wins 287 to 251. If he also loses Ohio, he ties 269 to 269 (guaranteeing Romney a presidential win in the House vote but making it possible Biden retains V.P. in the Senate vote).
Based on where the RCP swing states are, the 2004 map is possible, with the New Mexico exception. Every other state is in the same position as 2004 or is a toss-up.
That's a good insurance policy. Nobody wants Biden as the VP. If something were to happen to Romney then Biden would be the POTUS and the Speaker of the House (hopefully Republican) then becomes VP. Right?