A few threads here have postulated what could happen in Persia and Central Asia if the Arabs fail to break through the Zagros into the core of Persia. But what happens to the Caliphates in that scenario, in particular the Umayyads? Persia and Khorasan were the power bases of the Abbasids. Are there any other areas from which the Abbasids could potentially stage a successful revolt, in particular if Mesopotamia is retaken by whichever dynasty replaces the Sassanids (let's be honest, without Mesopotamia to fall back on the Sassanids aren't ruling Persia for much longer)? Or do the Umayyads just limp along until the resentment of the Umayyad realm's non-Arabs, especially of the mawali, boils over?