If I was Calgary, I wouldn't be so much going after Zucker, you need a true 1st line Center, and or a 1st line Winger. Someone like Rust could be high value for Calgary.

Calgary would also be a great fit for Klingberg. (They need a 1st Line D.)

The first line has been the least of their issues this year. I can't see PIT selling since they're comfortably in the playoffs. CGY previously had interest in Zucker and it feels like PIT is willing to let him walk for next to nothing. His advanced numbers are still good so it could be a solid cheap add for them to round out their middle six which they need without moving big assets.

to answer your question.
The penguins would not retain in moving zucker.
They just don't have that kind of option cap wise next year.
You are right in saying they would possibly move him at next to nothing.
When that happens is the question. Offseason, sure thing. By TDL....that's a little trickier as they need to find a LW to replace him then. Which again hits at their cap issues moving forward.

But either way, retaining isn't an option for them.

Lol we already have two RD better than Klingberg, and Hanifin’s better as well. And our first line is arguably the best in the entire league this year. Rust would be nice for our 2nd line but Pittsburgh isn’t trading one of their best players for futures when they’re in the playoffs, which is the kind of deal we would want to make. Zucker could be a change of scenery hockey trade, but the only guy that makes sense to send the other way is Lucic, who I like more than Zucker honestly.

Hextall has gone on record saying he's only looking to make hockey trades and not add incentive for teams to take his players. Next season is his last season under contract, so the Pens really don't have pressure to move him right now and in the off-season probably have a better chance of making a mutually benefiting move with another team.

EDIT: That said, I don't know that these two teams are much of a match for Zucker. If the Pens didn't have a logjam on defense, I could see a Zucker/Zadorov swap since Hextall has been looking to get more physical.

Calgary should have zero interest in Zucker. We dodged a bullet a couple years back