The main reason I don't think JJ will revert back to his old habits is simply because, IMO, he is a very smart guy.
By that I mean both business smart as well as common sense smart.
You can see how he never wants to be in cap hell again. He's stated that many, many times.
He knows his weaknesses, which are also his strengths - i.e., he's a wildcatter (sp?) and risk taker at heart, when properly channeled, is a huge strength.
We know JJ learns from his mistakes, which is one of his most positive characteristics.
This may sound like not a big deal - learning from mistakes - but look at Snyder, as an example. The team continues along the same path, so it seems, year after year after year. Still in cap hell, still overpaying for marginal talent. Sure, they made the playoffs this season, but I don't think their model is sustainable for the long or medium run.
I think what we've been doing for the past couple of years is a sustainable and winning model for the medium and long run.