I can't stand the narrative of, "should the Penguins be sellers or buyers?"
They need to be better. Full-stop. Addition by subtraction in some cases, so sellers. Adding legitimate young talent via trades, including high draft picks, so buyers.
If Crosby, Malkin, Letang and Karlsson want to be Penguins, then they will accept the moves if they improve the team. They are all smart people, so they know this roster is just not good enough. They also know that the GM has precious few assets to work with.
Whatever happens, this team CLEARLY needs to get YOUNGER. These are not the 2002 Detroit Red Wings. This team cannot compete as presently constructed. So, trading away Pierre-Olivier Joseph (the second/third-youngest player on the team) is nonsensical. Start with veterans, please. And sure, if Guentzel wants to stay and the contract does not damage the future of the team, you can re-sign him too. Top scoring wingers are hard to find. This team (arguably) only has one. But, if you can improve the top six by actually trading Guentzel, then go ahead. I think it makes more sense to try to move the other top-six options: Rakell, Smith and of course Rust (which is tricky because of the contract language in his deal). It also makes too much sense to move Eller, who should have value, Nieto (Edm nearly signed him last summer) if healthy and Ruhwedel (I doubt he has value beyond what Mike Sullivan sees, but perhaps somebody else thinks like him). Nedeljkovic is also a potential trade chip, but timing is always important when moving a goaltender.
If this team got younger, chances are they get better. The veteran core has to believe, and of course the coach is a non-believer, but Dubas has a chance to do some good things here.
Don't eff it up.