Mitt Romney, ineluctable or unelectable?

If not Romney, then whom? It’s probably going to be Romney, but there is still that tantalizing possibility nobody secures enough delegates to win on the first ballot, and, when no longer committed to vote for a specific candidate, some deal is cooked up behind closed doors. Would the nod then go to Santorum, Gingrich, or one of those who dropped out early? Is there anyone in contention who is more electable than Romney? Is Romney electable? If there is a brokered convention, what chances do you see for a dark-horse candidate to be nominated?