I read an article earlier that divisions are beginning to appear in Arab sunni groups fighting alongside ISIS in Iraq. Very likely ISIS won’t make it alone. However, so far they all seem united in overthrowing Maliki’s gov’t. But not all wanting an Islamic caliphate per ISIS’s ultimate goal. I see parallels with Khomeinist revolution in Iran in 1978-79. Different groups joined Khomeini’s supporters to overthrow the Shah. But once that objective was met & Khomeini got control, he executed many who had supported him but weren’t directly part of his Islamic circle. They just have to make sure ISIS doesn’t achieve what Khomeini did.
The Baathists who worked for Saddam are conspirators par excellence. I doubt they're in any danger of being surprised by ISIS.
Surely there are plenty of tribes and citizens who will be looking for revenge against ISIS’ butcherings and mass murders. All it takes is ISIS butchering someone from the wrong tribe or family and they make a lot of enemies - perhaps entire provinces. This I believe was part of the strategy Petraeus successfully used to build local support for coalition operations against al Qaeda.
Watching ISIS break apart will be kind of like putting scorpions in a bottle and watching them fight it out. We need not and should not choose sides but leave it up to the Iraqis to sort out which scorpions they are willing to be ruled by.