“You have appealed to Tash,” said Aslan. “And in the temple of Tash you shall be healed. You must stand before the altar of Tash in Tashbaan at the great Autumn Feast this year and there, in the sight of all Tashbaan, your ass’s shape will fall from you and all men will know you for Prince Rabadash. But as long as you live, if ever you go more than ten miles away from the great temple in Tashbaan you shall instantly become again as you now are. And from that second change there will be no return.” (The Horse and His Boy)
Rabadash behaves very badly and is turned into an ass. He is given one chance for reversion back to human form, but if he throws that away and strays too far from his god, he will revert to being an ass forever.
As an alcoholic, I became an ass. Whilst I remain close to God, I am human again. If I stray, I will revert to being an active alcoholic, and it is unlikely I would be brought back from that.