Right about now, we can be forgiven for focusing on the Burning Legion and the threat they pose to Azeroth and the universe. Even if Sargeras was defeated utterly, the vast army of demons at his disposal will likely remain a threat. Although Archimonde and Kil’jaeden are seemingly disposed of, this vast worlds-destroying force is a monumental adversary.
And of course, even if the Legion were neutralized, there are still threats such as the Void Lords and the Old Gods. Even if they were somehow dealt with there are plenty of other menaces to be faced. Other rogue demons, the Scourge and the Lich King, and many worlds we know nothing about.
But for my money, one of the biggest threats to Azeroth is Queen Azshara. She’s dealt with both the Legion and the Old Gods and retains her own will, her own purposes. Even now with Azeroth on the verge of destruction she has her eyes fixed on the main chance. Azshara cares for one being, and one being only. Herself.