Might I add, however, that if civil war does break out there is little reason to expect that the ultimate solution will prove that far different. There is little evidence that the Shiites would be capable of subjugating the Sunni, and in fact it's quite likely that the Shiites would fracture amongst themselves. Most likely, the Kurds would swiftly move toward independence, Baghdad would become a bombed out shell like Beirut, and the Arabs would pound on one another until they exhausted themselves into some kind of agreement.
I think you have it right, more likely than not, unless neighboring states get into the act, one way or the other. What we need here is a bit of luck. There is a relatively good outcome out there about one to two standard deviations from the mean on the right side of the bell curve.