Okay, let's pretend that Justinian chose to not conquer the west for whatever reason that is (anti-barbarian sentiment, I don't know) and focus in the eastern border with Persia. The effects of the plague are less worse than OTL and the empire was able to survive the arabic conquests (but the Sassanids fall anyways).
The byzantines crush the attempts of an arabic conquest of Egypt and Syria because they're stronger and the Persians pay the price. In the future, is it possible for the empire to declare war against the arabs and conquer the rest of Mesopotamia, restoring the original Trajan borders? Maybe during a independent islamic revolt in Persia or something else that could break the Caliphate in several states like OTL. What are the challenges to be faced?
The byzantines crush the attempts of an arabic conquest of Egypt and Syria because they're stronger and the Persians pay the price. In the future, is it possible for the empire to declare war against the arabs and conquer the rest of Mesopotamia, restoring the original Trajan borders? Maybe during a independent islamic revolt in Persia or something else that could break the Caliphate in several states like OTL. What are the challenges to be faced?