To be honest, I'm not sure the Sassanids were in good shape even if they defeat the Muslims at Al-Qadisiyyah. Any empire that collapses so quickly as the Sassanids did must have been rotten to some extent in its core. Certainly after the death of Khusrau II the empire experienced a protracted period of instability which led to the accession of an 8-year old boy to the throne of the Empire. And it's not like the Arabs hadn't been defeated before by the Persians (the Battle of the Bridge). My guess is after al-Qadisiyyah they'd just try again after a few years, this time with a better general like Khalid ibn al-Walid or something.
Last edited: