When Heraclius defeated Khosrow, Iyyas presenting himself as the last Lakhmid joined the free Arab state of Old Medina and a revenge attack against the traitors of Al-Hira.
But until his death he Iyyas was still just one of many Nabis of the Sabian faith who had learned Gabriel's Ecclesiastical poetry.
After the Byzantine Victory of 622, these Baptists did present their faith to Heraclius as the Hadiths claim but there was no leader by the name of Muhammad to be heard of according to the Byzantine version of the story. In fact, the belief presented was Monophysitsm and the presenter was called Paulic (its adherents came to be called Paulician by the Byzantines ever since). But Heraclius decided he knew better and came up with his own idea which he called Monoenergism.