Rust annoyed the living daylights out of me frequently last season - and the prior couple - with the way a once buzzsaw player seems to be trying to be diet Kessel, but he did make Geno's line better last season. I wish he'd spent more time with Geno and less with Sid, but Sid's line got good results too. I'd happily move him in a heartbeat to free up space for a better player, but he's not a problem.
And even if he didn't have trade restriction, I don't think guys giving up a big dog would hugely want him.
I think if a big dog did become available, the Penguins' route to obtaining him would be one of
a) Trading Guentzel, who has zero trade restrictions and is highly fungible
b) Giving up the farm
c) Pay through the nose in FA (the guy isn't there in FA)
Right now I'm thinking there won't be one available, and the team should try and keep assets back in case for flexibility and proceed to fill the roster with good value guys who can be like Zucker - unrelenting effort, enough skill to score freely for their role. You know, super easy to do.
Incidentally... if Colorado made Girard available, how would guys feel about targeting him?