For the first few WoW expansions, we were dealing with truly existential threats to Azeroth. The Burning Crusade admittedly snuck up on us - most of the expansion was built around dealing with the Illidari and Illidan himself, even if the Betrayer barely showed his face during the expansion (and as we'll learn in Legion, he was probably the wrong person for us to fight.) Still, that expansion ultimately ended with an invasion by the Burning Legion.
Sunwell Plateau might go down as the hardest raid in WoW's history, but ultimately, one gets the impression that Kil'jaeden's attempt to fight his way in through the Sunwell was a rushed attack of opportunity - Illidan's seeming complacency (something that has now been revealed to be his working on a big plan) drove Kael'thas to ally with the Legion, but this had to have been within a few short months, and big of a threat though it was, the invasion at Quel'danas was, in my interpretation, the Legion bringing their B-game.
Wrath had us dealing with two existential threats to life on Azeroth. The first was actually partially of our own making. Long ago, Yogg-Saron had taken over Ulduar, but it was our killing of his most powerful minion, Loken (and man did Loken cause a whole lot of problems if you read Chronicle) that set off an automated system that could have seen Azeroth re-originated, meaning scrubbed of all life (Uldum, the facility that housed the origination device, was originally a lush jungle. The Tol'vir activated it on a low setting tens of thousands of years ago and the place is still an arid desert. Now imagine that on a planetary scale.)
But of course the main event was the Lich King, who planned to cull the heroes of Azeroth until he had the absolute finest and then raise them from the dead to serve as the generals of his campaign to sweep over the entire planet.
Probably the closest the planet came to being destroyed was Cataclysm. Deathwing, empowered and maddened by the Old Gods, set about undermining the very structure of the world, breaking barriers between the Elemental Planes.
We actually get to see a scenario in which he has succeeded in the End Time dungeon. The world seems totally dead - the only remnants of life are echoes of our lost heroes. Even Deathwing himself doesn't survive the Hour of Twilight.
The only truly living being we see is Murozond - the future, corrupted version of Nozdormu, who transformed his Bronze Dragonflight into the Infinite Dragonflight. Indeed, Nozdormu knows or at least thinks he knows that this is his eventual fate and actually aids players in what appears to be his own eventual demise.
I've addressed some of the complications here before - like the fact that we killed Murozond in a future that will no longer take place, which makes me wonder if he's still dead within the timeline. But what I'm concerned about now is Murozond's claim that he is preventing the "True End Time" by allowing Deathwing to destroy the world before we can get to that point.
According to the Dungeon Journal, Murozond has been corrupted by the Old Gods, much like Deathwing. So the huge caveat to all of this is that he might simply be operating on lies that they have told him.
That being said, let's assume that thanks to his time-travel abilities, Nozdormu really does know about a fate worse than a successful Hour of Twilight.
The immediate scenario to jump to is the Burning Legion taking Azeroth. The Legion wants to scour the universe of all life, but we discovered in Chronicle that there is an understandable, if insane, motivation for doing so. Sargeras wants to destroy Azeroth specifically because it A. is the host of a World-Soul, aka a nascent Titan and B. it is infected with Old Gods who could turn that Titan into a Dark Titan.
Sargeras is often called the Dark Titan, but it would be more accurate to call him a Fel Titan.
The Old Gods were created by the Void Lords - beings outside of our reality that are even more alien and incomprehensible than the Old Gods. The Old Gods were created in order to infect worlds with Shadow/Void energy. In theory, a World-Soul infected with this energy would become a Dark Titan. Given how dangerous the universe is when there have been benevolent Titans to shepherd it, consider how horrific it would be to have a Titan bent entirely toward evil. Ok, yes, Sargeras. But the thing is, Sargeras is motivated out of fear of this thing. Sargeras, a massive god the size of a planet who has fought and defeated demons for eons. Azeroth is different - the chaos of the elementals is a sign of this. On Draenor, despite being a planet full of incredibly dangerous flora and fauna, the elements get along pretty well. But Azeroth's world-soul has drained away so much of the "spirit" element that the elemental lords constantly try to war with one another.
Sargeras wants to kill Azeroth - not just the people on its surface, but the World-Soul within - before such an eventuality can come to pass.
So here's a question: how is the victory of the Old Gods at the Hour of Twilight preferable to the Burning Legion coming in and destroying Azeroth? Obviously neither's good for anyone living on the planet, but wouldn't Sargeras at least be succeeding in preventing something truly horrific from happening? Doesn't the universe stand a better chance fighting off Sargeras than a Dark Titan Azeroth?
If the Legion's arrival is the "True End Time," is it really worse?
I think there are three ways that it could be.
One is that we're wrong about what Murozond is talking about. That some other even more horrific thing is farther down the line for Azeroth. It's hard to imagine things worse than the Legion or the Old Gods winning. Maybe a back-to-evil Lich King allows the Shadowlands to swallow up the universe and death overtakes all things. Who knows.
A second is that we've been interpreting Deathwing's actions in Cataclysm all wrong. Yes, he has been driven to insanity by the Old Gods. But consider his methods - he basically was trying to scour the surface of the world using the powers of the elements. That sounds a little like what the Reorigination device was intended to do, so why didn't he... oh yeah, he totally did try to activate the re-origination device. That's what, like, half of the quests in Uldum are all about.
What if Deathwing wasn't actually trying to help the Old Gods? What if instead he was fighting back with the last little bit of Neltharion that remained within his mind to finally put a stop to the Old Gods on Azeroth? Oh, sure, he had to be stopped because he was going to kill everyone on the planet, but what if "End Time" is not actually a picture of the Old Gods triumphant, but instead a picture of an Azeroth that was burned to a cinder - mortals, dragons, Old Gods, and all. Perhaps what we were seeing was Deathwing succeeding where Sargeras has failed time and again.
Then there's a third scenario. Sargeras created the Burning Legion in order to fight the Void. He has an army of demons whose purpose is to burn away all life in the universe to save it from corruption.
That's his stated purpose. It might even still be what he believes.
But consider that Sargeras' main enemies when he was a part of the Pantheon were the very demons who he now commands. This is a guy who can compromise his principles when it suits his purposes. Sargeras has no compunction using the creatures he had previously considered the greatest threat to the universe.
So why the Fel is the Legion using so much Shadow magic?
The Legion's entire purpose is to prevent the Void from getting a foothold within the physical universe. Yet among its ranks are plenty of Voidwalkers and half of the magic the Legion uses is Shadow-based. If anything, that seems like it would do more to help the Void Lords than hinder them.
Consider also that the way that Sargeras found out about the Old Gods was that he found a Nathrezim serving them on another planet. Demons clearly have no problems working with Old Gods.
There are two explanations I can think of:
First is that Sargeras has totally lost perspective - he's gotten used to using his "enemies'" weapons and so using Shadow magic no longer sets off any red flags for him. In other words, he's gone insane, and it's possible that the Dreadlords have been manipulating him all this time, serving their true masters, the Void.
Alternatively, maybe we're giving Sargeras too much credit.
The thing that made Sargeras turn on his fellow Titans was not so much their disapproval of his destruction of a World Soul. No, it was when Aggramar told him that there was a World Soul that would be more powerful than any living Titan. Aggramar told him about Azeroth to try to encourage him and show him that there was hope for the future.
Instead, Sargeras cut him in half. For eons, Sargeras had been the mightiest of the Titans. He had been their star, their champion - more or less the most powerful being in the universe. And now he was confronted with the possibility that this "Azeroth" was going to outmatch him.
Perhaps Sargeras and all of his evil - the evil that led to the destruction of Draenor and countless other worlds, the rise of the Undead Scourge, the exile of the Draenei, and presumably billions if not trillions of deaths and countless souls corrupted or consumed - is born out of pettiness. Sargeras doesn't want to be upstaged by some new Titan.
And that explains why there is nothing Sargeras won't do to destroy Azeroth. Maybe he doesn't care about the Void or the Demons or anything else. He just wants Azeroth dead.
And Murozond might have seen that his actions lead to the exact thing he would fear most - a Dark Titan Azeroth who emerges and snuffs out all light in the universe.