What if the Rustumids managed to survive?
Now for a point of divergence I imagine what if the ibadi Rustumid state instead of going into decline and shifting from a consultative imamate into a hereditary state that was seen as increasingly tyrannical by the population.
Instead the state maintained it's consultative elective model for electing new imams through piety and competence and under proper leadership that is not threatened by a hereditary succession crisis managed to build up an army and pushed back the Fatimids who were not able to take Tahert and thus the Rustumids survive and gain prestige and possibly become a sort of buffer state in the middle of north Africa that keeps the Fatimids in check and possibly allies with other Islamic states to the west like Cordoba and the different dynasties rulling in Morocco.