For a clue see this article:
Iranians recently had a foretaste of possibilities. If Khamenei should conclude that the only way to retain power is to totally unleash his security forces Iran’s people can expect Diyala-like excesses. Khamenei’s past crimes reveal his Machiavellian philosophy of rule: “It is better to be feared than to be loved.” That is, let the people may sulk so long as they obey.
Khamenei may never fully suppress hostile graffiti, chants, videos and slogan-filled currency but he can put up with them if that is the best the opposition can do. Present “restraint” comes not from any moral scruples but from fear that Khmer Rouge level of violence would substantially reduce perks for the in-crowd. The gloves will come off when the regime’s brutality have radicalized enough people to the point of violence.
Watch for organized and armed resistance movements by minorities near porous borders. Elsewhere watch for radical and secretive gangs similar to extremists in Germany, Italy and the USA in the late sixtiess. Lacking military training and weapons, such groups will rely on assassinations and fertilizer based bombs.
Laws, courts and constitutions limited the responses of western government while Iran’s Islamist rulers face no such handicaps. If need be, they will not hesitate to murder millions if that’s what it takes to survive. Consider how this regime took advantage of a parliamentary bombing to kill thousands of unarmed people (leftists) merely for having the wrong political sentiments. That sufficed to qualify for executiion even if one had no contact with radicals.
Today’s opposition is much broader and exponentially larger. Therefore a similar approach would require an exponentially larger number of victims.