Two things to look for in a revolution are the moment when the leader or leaders of the ancien regime suffer a sudden loss of nerve, often due to the sudden realization that their position is less secure than they had peviously thought. (Think of James II when Marlborough crossed the field to join the forces of William and Mary or of Nicolas Ceausescu when he suddenly realized that the hundreds of thousands of rent a crowd people he had gathered up for a pro- government demo in front of his palace were chanting anti-government slogans, or of Ferdinand Marcos when part of the leadership of the Phillipenes army came out in support of Corizon Acquino). At moments like that, the old regime leadership start suffering vicarious flashbacks of previously overthrown leaders: Charles I on the scaffold, Moussolini hanging upside-down from a lamp-post, etc. and start looking for the nearest exit. When that happens the game is over and the revolution quickly replaces the disintegtrating ancien regime.

The second possibly determinative development would be for key members of the current leadership to somehow fall into the hands of the revolutionaries (as happened with Louis XVI , Tzar Nicholas, Moussolini, and Ceausescu). This almost always changes the dynamic of the revolution, generally by reason of execution of the outgoing leadership. Obviously Khamenei and Ahmadinejad will be taking precautions, but if they can’t trust their own Revolutionary Guards Corps officers, anything could happen.