I have always liked Quinn and when healthy he is the best in the business. There is nobody that turns the corner like he does and he is held every down. Keeps attention away from Donald.
Still 12 Mil is a lot for a guy that can't play full time and whose production has been dwindling. I don't think you can trade him with that salary.
If I had a good feel for his health I might keep him for he is still young and has shown great form in last 4 games.
But if health is in doubt or I feel he can't be a full time guy I think you have to cut him.
I doubt an extension will work. You would need to increase guaranteed money and add years at a reduced price of say $8Mil per year. and you would still only get him down to around 10 per year. That doesn't work for me.