I am not sure things are as clear some might suggest but we are moving from the literature on electoral fraud to the academic debates on repression, social mobilization and regime maintenance. I don't know anything about Iran, but the question, as always, is will the young guys with guns fire upon the citizens? What do the citizens (especially the protestors) expect? What does the government expect? The reality is that no one can be confident about what happens next. If the Interior Ministry successfully gets the police to shoot, then the question will become--will the Army fight the police or the people or stand aside?
The more we know about the stuff, the less confident we should be about any predictions. So, my prediction is that we will not know what will happen until it has happened.