GM'ing 101 you do not let top 5 players at their position walk, because they are so hard to replace. You sacrifice the middle class of your roster if need be. The funny thing is the Panthers have the cap space, Gettleman got offended in negotiations, and thought his genius could overcome it. This a Baalke, Tim Ruskell type move, you don't mess around with elite talent. You either extend, or franchise tag them.
I remember people saying the Seahawks couldn't keep Kam, Earl, and Sherm, but Seattle bit the bullet, and sacrificed some of their middle class to keep their elite players. An aging Chris Clemons, and Red Bryant were cut to help handle Sherm's, and Earl's massive contract bumps. (Mainly Sherm's going from a 5th rd rookie contract to #1 Corner money.)