Villa fans seem convinced that JWP will have a release clause in his contract now because he has the same agent that Grealish had, and that he'll be leaving next summer.
It's also the same agent that JWP had when he signed a new contract last season, as far as I know, and that appears not to have had a release clause.
If there is one, I reckon it'd most likely be a very high one, or a relegation release clause, otherwise, like you say, his last contract still had us in a very strong position.