If it goes to the convention I foresee total gridlock, and thus I think it's more likely Newt and Santorum would throw support behind an entirely new ticket (i.e. one without either of them on it) that represents their constituency reasonably well. I suspect the strategy would be a geographic play to lock up two of three between VA/NC, WI/MI/OH or CO/NM/NV. Given that my guess is McDonnell / Daniels.
That's my thought as well, although I think Gingrich/Santorum might try for a ticket with just them if they've got 50% between the two of them.
Unless Paul were to throw his support at Romney, I don't see Romney winning a contested convention. There's simply too much "Anyone but Romney" sentiment out there for ROmney to get it any other way.
Frankly, I think a lot of conservatives are misreading "the GOP Establishment". For the most part, they don't like Mitt because he's Mitt. They like him because they just want to win, and they think he was the most electable guy. But I think the depth of the "Anyone but Romney" sentiment probably has caused some of them to reconsider that, and look for someone more acceptable to the party as a whole.
If Marco Rubio is not on the Ticket in the VP spot we lose Florida. If we lose Florida, we lose the White House. Plain and simple.