He is A problem but maybe not THEE problem.
He did this when he signed his $3.5mil deal - he was absolutely unconsolidated trash the next year. He bounced back, though. At his age and current deal though, I think there's less incentive for him to push anymore.
The problem with the likes of Rust, Zucker, and Rakell is that the moment you let them walk in free agency, your immediate need becomes exactly who they are.
If I'm Hextall or any other new GM, this off-season, I make an ominous phone call to Rust direct and ask him "are you willing to waive your NMC for any team, and if so, who?" Whether you intend to trade him or not is irrelevant. That will send a mental wake-up call that Rust desperately needs right now. I'd also be getting with Sullivan telling him to send him to the 3rd or 4th line occasionally.
The biggest issue right now is that there are no consequences for his lack of production, poor play, and drama. There is zero fight or intensity in the man and he gets top line minutes.