Chicago has the perfect situation for a total rebuild/reload/retool . . . whatever you want to call it.
New GM and coach and no expectations from the owner, fanbase, or media for immediate success.
Brand new young QB who isn't going to be barking about not wanting to be part of a rebuild.
Create as much CAP space as you can to allow you to be flexible in acquiring talent, and accumulate as much draft capital as possible to give you lots of draft lottery tickets to find winners to add to your roster. Dumping Mack makes complete sense. Not re-signing costly veterans like Alan Robinson, also makes sense. He's still relatively young and will want a big contract and doesn't want to be part of a multi-year rebuild. Take your COMP pick and use it wisely.