Let's have some fun.
I tried to dig into what a Patrick Kane trade might look like. I don't think there's a such thing as an over-the-top trade in hockey but this might be close. It would be shades of Iginla to Pittsburgh in 2013 and we know how that worked out for Pittsburgh.
Let's start with Kane. The first hurdle is his full no-move. Given he's a 3-time Cup winner he may not want to chase a 4th, or may not prioritize winning if he does agree or want to be moved. I have no clue what he thinks of Boston. He's from Buffalo and a lot of speculation has been he'd end up there in free agency or the Rangers. At the very least, it willing limit his trade market. The next factor that will limit his market is the $10.5 million cap hit. The maximum Chicago can retain is 50%, so it'd be $5.25 million in that case. In terms of actual cash owed, he's pretty cheap. Chicago paid him a $4 million bonus in July and thus his salary this season is only $2.9 million. Acquiring team would only be responsible for the remainder of that salary. I think the cap hit + no move is going to severly limit the market and also the return to Chicago.
On the Bruins side, the biggest hurdle is the cap. They are currently $1.3 million over the cap. Assuming Chicago retains 50%, that means the Bruins would need to move a minimum of $6.5 million just to fit Kane in. Reilly and Smith seem like obvious candidates to be traded and they combine for a $6.1 million cap hit. Reilly is already in the AHL and Smith can't get on the ice for Boston having only played in 10 of 19 ganes (1 or 2 games missed were injury related). Chicago may find some utility for Reilly. He's got an extra year on his contract, Chicago is thin on D and could see him as a pump and dump candidate at next year's deadline. I'm not sure they'd be all that interested in Smith as a pending UFA unless the deal came together in advance of the deadline and Chicago could flip him elsewhere. I think it would make more sense for the Bruins to move these 2 in other deals though. Chicago would probably view both as having negative value and thus increase the return to Kane. The Bruins may be able to squeeze out some value elsewhere for Reilly and more likely Smith.
As for the actual return to Chicago, I don't think it'd be an awful lot. The best we can use for a comp is the Giroux trade last season. Very similar circumstance. Franchise legend with a big expiring salary on a bad team. That trade was:
To Florida: Claude Giroux 50% retained, German Rubstov, Connor Bunnaman, 2024 5th
To Philly: 2024 conditional 1st, 2023 3rd, Owen Tippett
So a top pick a minimum of 3 drafts a way, a mid round pick a year away and a post-hype prospect in Tippett is all it took to get Giroux at 50% retained and a couple of AHL fillers (Rubstov a poor mans Tippett- former 1st round pick who struggled mightily in the AHL).
I bet a future first would be more than enough for Chicago. 2023 is reportedly a deep draft but if I was Chicago a 2024 or 2025 draft pick from Boston might be more appealing given the window for Boston. I'd rather roll the dice on that then taking a pick that's likely in the high 20's this year. Toss in a mid level prospect and I think that'd wrap it up.