As the title states. WI John I, the Byzantine emperor that reconquered much of the Levant before his death in 976, lived. If he lived, would his conquests be solidified against the Abbasids? Could he even retake Egypt? What would the effects be on the long term health of the ERE? He died at 50 IOTL. Let’s say he avoids death until he’s 70. It is claimed that he was poisoned, so let’s say that plot is foiled and his short reign is prolonged by twenty years.