Rick Santorum’s only hope right now is to team with Newt Gingrich. Santorum needs to talk to Newt and say, “look, we need to team up. You and I on the ticket together. Right now. Otherwise Mitt Romney ties up the nomination in April.”
Will it happen? Doubtful, but if not, there is little chance for Santorum in the long term.
(Of course he could do the same with Ron Paul, however the differences in their positions make that seem unlikely).