Bears are gonna be able to block any move to Chicago media market, I'm pretty sure. Don't think they'd have much luck luring a NFL expansion because of that.
But it already is a top 10 (in revenue) concert venue for large venues. Obviously they'd have to compete against the new Bears stadium in Hammond or Arlington too. But it would probably do okay. And it could aggressively court itself for international soccer matches, and have no scheduling conflicts without Bears and Fire.
But Bears and Fire both leaving will undoubtedly be a big hit. I'd imagine it can still clear enough revenue to pay it's upkeep costs for a while at least. At some point in the far future that probably stops being the case, and then it's teardown and parkland, which really is what the site would be best for.