Once they are out of the race they can take shots as much as they want...they don't have much to lose by doing so unless they are angling for a cabinet position, in which case they are more than willing to do Romney's dirty work.
I doubt Romney will be picking Bachmann for a Cabinet position. Moreover why would one take someone who was totally ignorant with them and give them a position.
Oh I'm not saying he would give a shot to Bachmann. I mean that other candidates can afford to snipe at Gingrich and others since they are out of it, and by doing Romney's dirty work they might raise their standing in his eyes. I don't expect to see Bachmann in a cabinet position

but stranger things have happened.