I cant see how signing Bennett shuts the Panthers window.
This isnt the Leafs locking in their core 3 to huge deals at the time, and signing Tavares later, eating up a significant amount of their cap.
The Panthers have their captain, and one of the best players in the world, locked in to a ridiculous deal, and everyone else has followed suit behind him. And if they dont, Zito will replace them, as he has done so far more successfully than not.
Why make the comment about the Leafs you say? Because the Leafs deals happened when the cap was lower, and saw minimum rise because of the reasons we know about already, and have hampered the teams ability to build a better team around their core. While with the Panthers captain taking less, everyone else lining up behind him, and the significant cap increase over the next few seasons, will allow them to sign Bennett, and still build around this core.