John Vatatzes, Emperor at Nicea

He died in 1254. Suppose he lived longer, at least until 1265 or 1270. Would Michael VIII still have been able to seize the thrown? How would western Asia minor have fared, if John had reconquered Constantinople from the Latins?
 
IIRC, he had epilepsy, which attack of was the cause of his death. I don't know if he'd be able to live much longer than OTL. Besides he was 62 or sth years old. Not mentioning that his son also had epilepsy...
 
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