The fact that Chicago got Fluery for free (minus the cap expenditure obviously) is quite immaterial.
His worth as an asset is no less than it was when he was with Vegas. If he retires its really no skin off Chicago as far as cap goes and he won't be able to sign with anyone next year...so if Pitt wants him that's obviously not good.
If Pitt wants him they are going to have to pony up appropriate assets. Though I hope he suits up for Chicago. I've always liked the guy and I'd rather be cheering "Flower!" than bemoaning "Flower!"
Your logic is absolutely nonsensical:
1. If Fleury could return something of value for Chicago, Vegas would have just traded him for that kind of value instead of giving him up for nothing. Why couldn't Vegas have just traded Fleury to Pittsburgh for the "appropriate assets" instead of just giving him up for free to Chicago?
2. If Fleury does not want to play for you, your 2 options are to trade Fleury or get nothing for Fleury and force him into retirement. How can you possibly think "we can just force him into retirement if you don't give us good value for him" is at all leverage? That's downright nonsense. That's not "leverage", that's "spite" and every player in the NHLPA would immediately put the Hawks on their shit lists for pulling that kind of stunt.
Here are Chicago's 2 choices if Fleury decides to not play for Chicago:
1. Chicago doesn't trade Fleury, Fleury retires and Chicago gets nothing for him
2. Chicago trades him and gets something for him
You thinking "we can just force him to retire if you don't give us a good enough return" has nothing to do with getting value for your team and everything to do with spiting someone else. That's not leverage, that's the Hawks being an asshole
The "value" Chicago can get for Fleury is a function of how much salary of his the retain, that's it. If they retain half of his deal, they'll get some value because $3.5 million in dead cap space is worth a pretty penny. But that's solely where the value is going to come from.