Yeah, guys like Ladd, Byfuglien, Frolik, and Campbell sure turned into bums after they left Chicago.
They let guys go because they absolutely have to, and right now, Sharp is the only reasonable way for them to shed salary. Bickell will be tough to even get rid of, they can't let Hossa go because of cap recapture concerns, and everyone else aside from Sharp is either a core player or not making enough money for them to save by shipping them out. It doesn't mean he's on some big decline, he's just shot well below his career average this year. If he'd shot at that rate, he'd have a 26-27-63 line in 68 GP.
More than that though, he's a proven playoff performer. He's got 12 points in 16 games this year despite being on the third line, and 77 points in 110 playoff games with the Hawks. Might be slowing down a bit, but he's still pretty damn effective. And considering the bind the Hawks are in, I don't think we'd have to pay fair value to get him.