I suppose extending the war simply means that the Byzantines are that much weaker, as Persia got fully conquered anyway.
Persia got conquered less because it was inherently weaker, but because the war was decisively won by Romans, the relative quick latter part of the war being attributable to being invaded with subsequent consequences on dynastic stability and state credibility.
A longer war strongly implies that neither side is able to decisively win, possibly ending with more of a stalemate than IOTL, making the border regions both more militarized and Persia less weakened than IOTL (in spite of "being conquered anyway" historically, Sassanians did managed to hold an efficient enough resistence against Arabs initially, and it was not a given that they had to be utterly defeated IOTL, so ITTL possibly less so).