Pence doesn't have a chance with the quality of the crowd that looks to be in the Republican Primary. Plus, he might have to give up his re-election chances just to run, although he could give Iowa a shot, and if not successful, drop-out of the Presidential race and back to re-election.
He'd be a prime candidate for a cabinet post.
As for Romney, I think it's interesting, perhaps his handlers have him convinced he can pull a Nixon (General election loser in '60, Presidency in '68) or Reagan ('68 and '76 Primary loser, '80 winner), but he has nowhere near the political chops those men had. I don't think he pulls the trigger, it's also an odd move as it takes away the "Hillary is old" talking point, with Romney being a few months older.