Ron Paul has announced, and a very possible outcome if Palin runs is that she wins handily and quickly, but even in that scenario, Ron Paul does pick up a substantial number of votes.
Is Gingrich in your scenario? The likelihood of Romney doing better than last time is questionable, seeing that the one thing that Romney was most known for 4 years ago, Romneycare, is now something that Republicans all hate. Palin is I think the most likely, but Gingrich more so than Romney. And even Paul can make the case that he’s the true conservative, and he’s been around long enough.
RP picking up substantial votes? Really, he never has before.