Maybe. You could have it even earlier where Persia enters on behalf of a side in a civil war, sees the weakness of the state, and seizes Mesopotamia for itself.
Yeah. A lot depends on how exactly "the Mongols don't destroy it" impacts things - something like the Anushtiginid Sultante (what a mouthful...) surviving in Western Iran is less likely to do so right away than if the Mongols never ride west. But even such a relatively weak Iranic state is still powerful enough to take advantage of the situation.
Using the term AS for a reduced but surviving Khwarezm state, since it no longer contains that region, but is still (as Muslim kingdoms in this region go) impressive enough to take seriously.
That is scary. I presume (correct me if I'm wrong) this wouldn't be totally irrepairable - but we're looking at decades of extremely hard (and expensive) work to restore them to pre-salt flat status. I don't even want to imagine (for early modern people) how much effort it would take to get them back to good farmland.Scary thought: Since the rivers are elevated in relation to the land, almost all the lower lying land that was scoured with canals would turn into salt flats, making it almost impossible to farm.