I don't think there are any reasons why it can't come back. Rulers already fall to heresies all the time. Why not Hellenic?
hellenic paganism isnt a heresy of christianity, its a full blown religion that was systematically destroyed by christianity after it's risealso, one ruler who goes back to hellenic does not really strike me as all that provbable of the return of hellenism, there;s a reason julian failed