If being a fan of fantasy fiction had taught me anything it's that it's very hard to kill a being made of living shadow. My guess, we haven't herd… er seen the last of him.

There's actually 2 horns. One that was severed and got into the ground (With some kind of active magic) One that grew back and was on his head, and possibly was the one that flew off.

So, his influence could return.

Dead? Alive?

Probably alive, but the fact he was freaking obliterated is still a shock; even if he's not quite gone for good.