Sullivan was always assumed because of the Tortorella connection and that's fried.
His success in Pitt was due in large part because he was very familiar with the roster and knew how to use them to their strengths. I have doubts that bringing him basically totally cold into this situation is going to yield much but disappointment. I mean he's been adaptable and squeezed juice out of that Pens roster for far longer than anyone should have expected, but does he still have the drive in him to start fully fresh in a shitshow? He's not that old, but he's also basically got nothing left to do or prove. Coasting to the traditional retirement age should be a concern about mindset.
Sullivan, Trotz, and Cooper are the trio of coaches who I thought really took their rosters to a higher gear with usage and systems/planning decisions, but it's been almost a decade since that peak which occurred in very favorable circumstances for him.