I think it's extremely unlikely that he's not dead. If Prigozhin were to surface elsewhere in the world (e.g. Africa), Putin would be even more of a laughing stock. Putin simply wouldn't risk anything less than absolute certainty.
However, I doubt that Prigozhin was alive when the plane took off; most likely Utkin and Chekalov were dead as well. Best guess is that the three were killed the night before.