Ah OK - that makes sense but not really from the Hawks perspective because they don't want or need a veteran over-30 d-man to clog up the lineup that should be used for young prospects. I wouldn't be surprised if they do a buyout for Brodie. Most Hawks fans hope to see Murphy go too - either this summer in a trade or at the TDL - they have a full cupboard of young d-men they need to play to get NHL games under their belts.
I know that the Hawks don't really want to have 5 years of Mayfield, but the point of it all is that you're either getting 8 or 9 years of Misa (or more if he stays into his UFA years) or 8 or 9 years of Desnoyers / Martone / Hagens / Frondell. If your GM and scouts truly think that Misa is just a whole level above those other guys, then you're going to be giving up something that you don't want to give up. Islanders have no reason to just give you Misa as a gift. Is being forced to take Mayfield a dealbreaker to get an amazing player? That's the question.
Regarding Connor Murphy... I'm very confident that if the Blackhawks did make this trade and added in Mayfield, the plan for the right side of the D core would be to play Murphy, whichever kid has a better camp out of Levshunov and Rinzel, and Mayfield as your three guys. Later, at the trade deadline (more likely) or offseason (less likely), Murphy is no longer a Blackhawk, and the right D becomes Levshunov + Rinzel + Mayfield. Then it stays that way for at least 3 seasons, maybe longer.
Regarding Blackhawks right handed D situation overall... I don't think the Hawks have any RHD prospects of note right now outside of Levshunov and Rinzel. Even if you draft one this year, that kid won't need waivers until 2030 (or 2029 if it's a late birthday). Between now and 2029 or 2030, Levshunov Rinzel Mayfield doesn't block anybody. So I don't think "clog up the blueline" is accurate, unless you're planning to move left handed kids over the right side. And hey, if something changes down the road and there's somehow a clog going on, there's always an option to buyout Mayfield in 2028 or 2029 if you can't find a way to trade him. It's overall a relatively manageable situation, albeit not an ideal one. If Misa is scoring 80+ points per year for you, I doubt you'll be regretting the trade.
Also, just to touch on the current crop of left handed D kids coming up for Chicago... this trade has Allen being moved out, which leaves Vlasic (obviously), Del Mastro, Korchinski and Kaiser all on the team by next summer. It's only 4 people, so nobody needs to go on waivers and nobody needs to be traded. If you think all 4 of them are too good to ever be the 7th guy sitting in the press box, then you trade one out. I've seen a lot of Chicago fans open-minded to moving Korchinski out, if they can get something valuable and young out of the trade. Either way, Chicago is going to have this same problem with or without adding Mayfield. In fact, the Mayfield trade removes Allen from the equation, which solves half of the problem right there. 4 left D to sort out instead of 5.