I would keep the 22 year old Dermott over the 30 year old Muzzin. He'll be cheaper and will probably be better in a year or two.His money needs to be put towards Barrie and Muzzin extensions. He's also a likely target for Seattle if they're both re-signed. It should be his last year here unless they open up cap space.
If you can get him on a 5 year for $3.75 AAV or under I think that’s a good move. A moveable contract if he struggles but also could be a bargain if he improves.