With Mug'Thol's lieutenants dead, all that remains is to kill Mug'Thol and retrieve the . I have no doubt he'll be reluctant to part with it. Most likely expecting you, too, given the... departure... of his fellows.
Find Mug'Thol, and deliver his head and the Crown to me. The Crushridge resistance will be at an end.
Three heads I have, a fourth I need. It will be Mug'Thol's, or it will be yours, <Name>. That I promise.
You have done your duty well, <name>. Mug'Thol's head shall adorn the highest peak of the ruins of Alterac, and the Deathguard will sweep the remnants of the Crushridge into the ground.