Yep, no reason to think this is a reality.
There's definitely a world where a massive trade like this makes sense for both teams. Let's ignore the Mercer+Holtz thing for a minute and just say we're willing to trade Mercer + significant picks/prospects. The plan could be for Hanifin to come in and eat the minutes Bahl has struggled to eat, then maybe trade Seigs in the offseason to free up the money to afford Hanifin and you also get an upgrade in goal that hopefully doesn't blow up in your face in a year or two. Hanifin solidifies the left side until Luke is ready to, and he is not a bad #2 after that. Our present D corp with Hanifin on the top pair and shifting everyone else down a peg is something I could see contending. It would be a huge bet to make by Fitz that this team could be a championship team and he'll figure out the cap in 2 years.
for Calgary, they probably can't get a centerpiece like Mercer by just trading one or the other, but as a package deal they can.
I doubt any of this is happening, though. And I don't care what we would be getting back, selling Mercer+Holtz would be a disaster that I just don't think Fitz would do.