Ok, there’s going to be a lot to discuss here.
Sylvanas is in league with the Jailer and started a war with the sole purpose of killing as many things as possible to fuel the Jailer and herself.
Death is the only thing the Void fears.
N’Zoth has been released and is of the Void.
Sargeras was attempting to corrupt as many beings as possible into fel-tainted demons.
Demons do not go to the Shadowlands when they die.
The Titans created Stone, Metal and Mechanized creatures that became cursed/gifted with the Curse/Gift of Flesh (Curse or Gift depending on the person’s point of view on the matter).
The Old Gods, Void Creatures, are the source of the Curse/Gift of Flesh.
Azeroth is a Titan waiting to hatch, and is likely corrupted by the Void.
Azeroth also has a nexus that ties it to the Shadowlands.
So in essence the Titans created constructs that could not die, as they had no souls. However the Curse of Flesh made these entities mortal. They bred and became numerous. Now, when those entities die, they empower an aspect of Death. So why would the Void, that fears Death, create something that empowers Death?
Sargeras found a way to stop the empowerment of Death by corrupting the souls of mortals and turning them into Demons. He also was involved in the creation of the Lich King, which holds mastery over Undeath. Is Undeath a form of Death? Or is it the destruction of Death?
We’re going to defeat N’Zoth early in the expansion, and then have to deal with the Jailer/Sylvanas. Caelia will likely take over as the leader of the Forsaken.
Sargeras will ultimately be released to deal with the Jailer.