If there is no release clause in Jack's contract, and I think we would have heard about it now, then I can't see him leave as a combination of two reasons.
1. He is worth more than we could get for him for us. There is no way we can get a world class player without Europe and he is our biggest marketing pull. Also he is good for 10-20 points more a season for us. In short unless someone offers us 300m ish it is not a really good deal.
2. Jack loves Villa like us and I don't see him rocking the boat this season, if any.
But I still hate all the stories that come out, and I get pissed with all the negative fans who try to protect themselves by being giving up and accepting defeat.