I hesitate to say too much about the goings on in Iran, but from my hazy knowledge the Sasanian monarchy was probably on the decline anyway, as was orthodox Zoroastrianism. So the Sasanians may well still be replaced, but it will be by another Iranian speaking dynasty with Iranian religious traditions, rather than by Arabs with Abrahamic religious traditions.
As for the Romans (the seventh and eighth century transition to the imperial period we recognise as "Byzantine" won't happen ITTL), it depends on the PoD, but in a scenario where Maurice and his heirs hold the throne, I expect to see further attempts to consolidate the Balkans in terms of military activity and more tries at creating an inclusive religious formula to bring the anti-Chalcedonian Christians of Syria back into communion. This will quite likely cause ructions in Italy and Africa.