From Pens POV it is difficult to draft up a Guentzel proposal without the result being lateral at best. Consider the fact the Pens window is realistically 2 (maybe 3) more years. Guentzel at 6 million for another year is potentially a huge piece of the puzzle for a 2024 run. There are no bargains like that on the market.
The minute you ship out Jake you have to replace his 40 goal production and above all his incredible chemistry with Sid. My gut feeling is Crosby would nix any trade that involves him.
If you do trade him, you need an instant impact player. Offensive prospects make no sense for the Penguins right now. Marner could make sense on paper (to replace production) but at a cost of 5 million more cap per year. That money could be used to address real needs (depth scoring, potentially another top-6 winger if Zucker walks) and again, I just feel it'd be a lateral move at best when you still have Jake at 6 million for 1 more year. Though, I will say with Marner his contract term fits the Penguins window, so that idea isn't incredibly far off - I just don't love it from a cap perspective. It's also a chemistry gamble though sure, he could be a great piece for either Sid or Geno.
For me the deal that would make most sense is to get a proven goalie who can step in from day 1 (Saros/Hellebuyck). Such a goalie would instantly become the best Penguins goalie ever (analytically) and give them an impact goalie in net to give them a chance for these last 2 or 3 years. Penguins still have to replace Guentzel's production but it could be done with the right moves and cap allocation. Whereas with Marner, his 10.9 mil cap hit is a stranglehold on other moves.