Hardy is a polarizing player, but he is not really much different than Ray Lewis. The only difference really between Hardy and Ray Lewis is that Lewis was viewed as a motivator, in part, because his team won a lot and he played for the Ravens, who seem to embrace fringe players who can play. Make no mistake about it, football is about winning. It is ALMOST the only thing that matters.
Having said the forgoing, it is qualified by two things:
1. Is the player such a bad apple that the team (or the league) will not to fade the p.r. hit for having him on the team; or,
2. Is the player so disruptive to the team that it outweighs the skill, talent and ability that he possesses.
Hardy is not unique in the sense that the NFL is filled with these types of individuals. The real trick to building a team is to find a way to manage these fringe type players and keep them in line enough to stay eligible to play and minimize their disruption to the team.
In a perfect world a team would be built with 53 Jason Witten type players. Unfortunately, that is just not possible. Hardy CAN play. He has talent. He is a one man wrecking crew. If you had a team with 53 Hardy type players it might be the most talented team in the league. But it would probably be difficult, if not impossible, to manage that many players with his personality type.
Winning makes it easier to manage this type of player, but it isn't a cure all. About all that you can do is to manage them as best you can, because they bring a lot of skill to the table and they can help you win. If they don't work out you cut them and move on.
Keeping Hardy on the team is the right move, for now. You try to manage him and see how it goes. You have experts who can advise you about how to best handle him, because you can't immediately replace his talent. But you look for his replacement that is more like Witten and less like Hardy. Signing him long term is problematic because players like Hardy are like a ticking time bomb. They usually eventually go bad. But keep in mind that every other team also knows about Hardy's prior issues. We can probably sign him to a bit of a discount because of his baggage. It is simply a balancing of risk vs reward.
Letting Hardy walk at the end of the season probably nets us an upper tier compensatory pick. I don't know what I would do with Hardy. Signing Hardy to a long term deal is dicey and would probably blow up in your face eventually, but his talent is undeniable. The Cowboys are doing what they should do, which is watching, evaluating, and weighing the risk vs reward. It is that simple.