Even though we may not help. Our presence in the region will prevent any outside forces from helping the mullahs oppress their people. If they start the killing, the people may very well finish it. We should put our troops on the borders to help the good refugees if necessary and to shoot the bad ones if we have the opportunity.
There are supposed to be units made up from Arab-extremists (Hezbollah types) that are augmenting the Mullahs' security forces. I don't think that these Arab battalions are going to have any problem slaughtering Persians in pursuit of some hardline Islamic theology.
The wild-card may be the Iranian Army. Whichever side that they come down on will win. I'm sure that the Mullahs are busily reviewing the 'reliability' of units in the Tehran area.
That may be just one of the contingency plans. Bush is/was smarter than he looks.