If the internal disorder of Rhomania is averted let's say by a a PoD that the treasury problems of Maurice are resolved by the lack of Sassanian peace payments and, thus the rebellion of Balkan troops that led to Phokas' rise is averted, and thus no justification (no dead Maurice) for Khosrau to invade the Levant, North Africa, and Anatolia, no reason for Heraclius to counterattack into Persian territory. From my understanding, a major component in the success of the Rashidun Caliphate's expansion was that the Byzantines and Persians were simply exhausted from fighting each other with major occupations of the opposing empire's territory that went far beyond any previous Byzantine-Sassanian conflict for 26 straight years, not counting the internal struggles going on within both powers (for Rhomania, Phokas' overthrowing of Maurice, which lead to the 602-628 war, his subsequent mismanagement and nepotism disrupting the state, and then Heraclius' overthrow of him in turn for Persia, Khosrau II's execution and the subsequent civil war as a result of the 602-628 war.)
