Dan Quinn would be dumb to not take a HC role. For one, it's a huge raise for most coordinators. It's not uncommon for a HC to earn triple what his coordinators do. And for another, second bites at the HC apple don't come around often. The league is becoming more and more hesitant to retread head coaches (a positive move in my opinion). So a HC job is not only a huge promotion, it's a promotion opportunity that rarely happens, and you have to strike while the iron is hot.
That being said, I don't really think Quinn is that good of a coach. He is competent, but he's not a game changer.
When he is given talented defenses like the Legion of Boom, or the surprisingly well-stocked current Cowboys squad, he looks good. But in Atlanta, he never had better than average talent on defense, and he never delivered better than average results. He is a competent whiteboard guy who switches up his defense and is willing to fit his talent to the scheme, but he's no Belichick. And he looks like a motivator now when times are good - the Cowboys players clearly love him - but he failed in a CEO role in Atlanta when times were bad. And that was after he was stripped of playcalling duties.
I'd like to see Quinn as the HC in Dallas... he's got a good thing going on this defense. He likes these players, they like him, they're succeeding, let's keep that ball rolling. And McCarthy is a total fraud.
But if you pointed Quinn towards a coaching-carousel job like say the Jets or the Panthers and said "turn this team around in 3 years", I don't think he's that guy to do that. He'd be smart to take a shot at it, but I wouldn't expect him to succeed.