Admittedly, I'm not quite as experienced in the hobby as many others on here but I think Mack's values are much more likely to trend downwards over time than upwards. His individual trophy case will, most likely, be remarkably lighter than his contemporaries. No Harts, Art Ross, and it doesn't look like he will pick up a Conn Smythe in this run either. Rocket(s) don't seem likely given he's never placed top 5 in goalscoring either. He's also no longer the clear cut best player on his own team with Makar there which I imagine only hurts his values but that's more conjecture on my part.
The positive is that Mack is still relatively young at 26, turning 27. While he's no ironman himself, neither is Makar, Rantanen, or Landeskog. His point production remains strong when healthy. Sakic and Forsberg both won Harts at ages 31 and 29 respectively. Patrick Kane won his at 27. He still has time but the clock is ticking. I happen to think, without any evidence, he'll win a Hart in the next 3 years but even if he doesn't he's a likely future HOFer and that's enough for me to have his cards forever.
This is all without consideration for the overall hockey/sports card market as a whole. If the entire market goes further south the rest of this year/next year then it won't matter as much what Mack has done. I think, in your shoes, I'd sell the more common cards and capitalize on the shorter-term prices and hold the longer/rarer stuff. Given your time in the hobby I imagine your cost basis is much lower than most so you'd still be making out well no matter what.
Anyways, I hope you found that helpful, thanks for reading!
