Victory on the Yarmouk is the obvious POD. The implications are not huge for Egypt itself (which operated more or less without change until Abd al-Malik), but very large for the ERE. You might see the grain dole restored to Constantinople, and the Empire's richest province will remain comfortably held. There'll be religious tensions, as ever, but I can't see these ever boiling out into any kind of serious revolt- it's very much in the interests of the landowning aristocracy and even the lower gentry to stick with the Empire.