I figure that if Michael didn't take him out the White Council definitely did when they heard that a Dragon got ganked and went to investigate everything related.
Maybe but I doubt Michael gave an interview. They probably heard a KoTC ganked a Dragon and figured it was above their paygrade. It actually does make one question just why a KoTC was sent there to begin with. Plenty of people get eaten, or destroyed by the Supernatural (just ask all the victims of vampires and ghouls), and a KoTC doesn't show up.
I forgot about him, I'd say there was a good chance he got his head removed some time ago. If not, he might be a foot soldier for the Black Council, but I don't see him as Cowl, I think Cowl has been around a lot longer than that.
Cowl does feel like he's got a lot of years on him, but Gregor was trading lives for power, and it's been decades. Over those years he could have gained a good deal of power, and knowledge by trading up.
Also he was already in the business of making deals with a freaking Dragon. I doubt Harry would have known how to summon one before meeting Ferro without Bob's help. So Gregor did have a decent amount of knowledge, and connections to be dealing with one.