WI: Rump Sassanid Persia after Islamic invasion?

Dorozhand

Banned
What if the Sassanid Persian Empire survived in the northeast as a rump state, holding off the Muslim invasions in that direction?
 
Even if the Muslims progression would be held by Persians, could they have supported the pressure from Turkic peoples?
I suppose that a Dabuyid-like dynasty could have held more lands, but I'm less sure about their survival.
 
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