A regime change is not going to be of the deomcratic variety. The mullahs aren't going anywhere. Ahmadinejad might get ousted, but Rafsanjani and his ilk would probably return to power.
Then the best we could hope for is that the 13th-Century Wing and the 8th-Century Wing of the Mullah Party fall on one another and teach each other to pieces.
Leaving the Pahlavis to walk back in, pick up the pieces, and return Iran to at least the 20th Century.