Both bad guys can be found around Mannoroc Coven, in the south of Desolace.
Although I have no knowledge of this Lord Azrethoc, I agree with Maurin, he must be stopped; especially if he is attempting to gain influence over the Burning Blade to further his goals.
You have already shown you wish to aid the Warchief, and I would trust you to gather a party to slay the demon lord and his warlock servant.
When you are ready, head directly south, and return to me when the threat has been ended.
Glory to the Horde, and death to our enemies, <name>!
The demons in Desolace pose a greater threat than ever before. My hope of returning to the Warchief dwindles as more and more of the foul creatures seem to appear.
I sometimes wish it was only the centaur we had to deal with.
A mighty victory for us all, <Name>. Let us rejoice in your success. I trust now that our future here is not as bleak as I once thought.
The demons will be slain, the Burning Blade will fail in their efforts, and we may one day have a place we can safely call home again.