You never know when you've dealt with a time-traveler.
In most portrayals of time-travel in fiction (whether it is even metaphysically possible is something that is still up for debate) a time-traveler experiences their own life in a linear progression like anyone else - their sojourns into the past or the future are almost like simply traveling to another place. The key difference is that an outside observer will perceive that person as not going through linear time, but rather popping into existence at one moment and then blinking out in another, even potentially arriving at the same general place at the same time - in a case like this, the time traveler will perceive this as two separate events, while an outside observer will witness one event with two versions of the traveler.
While we've done a little bit of time-traveling in WoW (we'll have to address Warlords a little further down) we generally experience time as a steady progression, always moving forward at a rate of one day per day. Events happen in order, and while there's a big old Warlords-sized caveat to this, we more or less see history moving forward into the future in the same way you'd typically experience it.
The Bronze Dragonflight is far more comfortable with jumping around in time. In the early quests you thankfully don't have to do anymore to get attuned to the original Caverns of Time dungeons, one of the bronze dragons (in high elf form) directs you to speak to a younger version of himself as if this were the most normal thing in the world. We can assume that this guy might remember talking to us when he was younger, and that somewhere in there he traveled back in time, aged a little, found himself in the same place and time he had been before, saw us show up, and directed us to take part in the conversation that, from his perspective, was years in the past and not like a minute into the future.
The biggest villains to the Bronze Dragonflight are the Infinite Dragons, and we got confirmation in Cataclysm that the Infinite Dragons are, in fact, those very same Bronze Dragons. The Infinites are future versions of the Bronze dragons - ones who have been, allegedly, corrupted.
That means that the very bronze dragons who we aid in defending the timeways will, one day, become the very menace that they have enlisted us to oppose. The only individual for whom we have seen both versions is in fact the Bronze Dragon Aspect, Nozdormu, who at some point will become Murozond. With Cataclysm timewalker dungeons this week, you might actually be fighting him around now.
Upon witnessing his own death in the End Time dungeon, Nozdormu reveals that this is the fate that was shown to him when Aman'thul imbued him with his powers. The intention, supposedly, was to humble him. Even with his power over time, he would eventually die.
Yet in a sense, I wonder if it was exactly mortality that he was being warned about or if it was something else entirely. Murozond represents the opposite of Nozdormu's purpose. The Infinites are all about changing the past. We get a clue from Murozond why they might be doing this - he claims that allowing Deathwing to destroy all life on the surface of the world could prevent the "True End Time," which is so horrific he doesn't even want to describe it.
What is this "True End Time?" My best guess would be a world in which the Old Gods succeed in corrupting Azeroth's World Soul and birth their Dark Titan. One would think that allowing Deathwing to succeed would hasten this plan, rather than preventing it, which makes Murozond's claims ring false. On the other hand, one could imagine that Murozond has been fooled - the Old Gods are master manipulators, after all.
Still, what if Murozond's intentions were not what they seemed?
At the time, the story went that Murozond was preventing the Bronzes from accessing other Timeways, intent on preventing the plan to retrieve the Dragon Soul before it was corrupted into the Demon Soul. Basically, Murozond forced all time travel to route through the End Time, and in order to get anywhere else, we would have to go through him. We wind up doing this, which then allows us to go back to the War of the Ancients, where we successfully retrieve the Dragon Soul and then aid Thrall in taking it to Wyrmrest Temple. It would seem that Murozond failed.
But what if he didn't?
Consider this: Murozond dies in the End Time. That is the death that Nozdormu already knew was going to happen - it's fate.
But what that really means is that the personal future - the vision granted to Nozdormu by the Titans - has been fulfilled. And as far as we know, that means that Nozdormu no longer knows any more about the rest of his fate than we do.
Yes, we know Murozond will die. But we don't know how much older Murozond was than the Nozdormu that we interacted with in Cataclysm. He - in both forms - is a time-traveler, and also, as a dragon, doesn't seem to age (or at least ages at a far slower rate - we do know that Senegos is seriously affected by his extreme age, but certainly the Aspects would be older than him, as there weren't any true dragons before them.) So Nozdormu could live another ten thousand years before he even becomes Murozond, and then Murozond could live another ten thousand years before he dies in the End Time.
Without knowing the entirety of Murozond's personal history, killing him has done nothing to actually prevent the acts that he had, from his perspective, already done. For all we know, Murozond had already spread the Infinite corruption throughout his flight and sent his agents all over the timeline to manipulate causality and by the time he got to End Time, he was already satisfied with his victory, and was simply accepting this fate because, well, he'd won.
There's another possibility:
While the Bronze dragons were charged with protecting the one true timeline, that implies that there are multiple timelines. We've already seen the War of the Ancients changed - with people like Rhonin, Broxigar, and Krasus showing up back then (there are even hidden quests in the Black Rook Hold scenario during the Light's Heart quest chain where you find them back then.)
The End Time does not actually wind up happening, because our actions within it allow us to travel back, retrieve the Dragon Soul, and kill Deathwing before he can pull it off.
When you kill Murozond, he does not leave a corpse. His body fades away. Why is that?
Well, by killing him, we open up the timeways he had blocked and are thus able to take the actions that prevent the timeline in which he died from ever happening.
So is he even dead?
Again, even if he is, our killing him at some unknown point in his personal future (it would be the end, but we don't know how far that is from Nozdormu's current age) doesn't really prevent him from doing any of the things he would have already done. But this might mean that even this death is something he managed to escape.
And then, there's another possibility:
What if Murozond isn't Nozdormu?
The time-travel in WoW was the messy kind - each action overwriting previous history, allowing for complex paradoxes to occur.
But when we traveled to a version of Draenor 35 years in the past, we had none of those problems. Why? Because that Draenor was a wholly separate Draenor.
And it wasn't a branching timeline, because the changes that Garrosh made to that timeline could not account for other changes - like the fact that there had never been any Garrosh B, the fact that Rulkan was alive, or other subtle differences that could not be accounted for.
What this tells us is that there are actually myriad, potentially infinite universes out there, and that each has its own version of reality. Presumably many are very, very similar, but have slight differences.
In fact, it's even possible that we didn't truly travel through time at all when we went to Draenor - time might have been moving at a just slightly different speed there (this would probably happen in a universe with a slightly different speed of light, for example) and thus our universe and that one were 35 years out of sync (a pretty tiny amount of time given how old planets and universes are.)
But regardless, the fact that there are all these universes was actually a big part of Kairoz' plan. Kairoz, a Bronze Dragon who helped break Garrosh out of prison and was aided by members of the Infinite Dragonflight, had a very different vision than Garrosh's Iron Horde.
Kairoz instead imagined that Draenor B would only be the first stop on their trip - that they would go to a Draenor C and then a Draenor D and so on and so forth, each time recruiting the same orcs to form an ever-larger, every more unstoppable Horde. An Infinite Horde, as it were.
And Infinite was literal - they would keep traveling to other universes and adding to their forces, creating a force that could rival just about anything in the universe - even the Burning Legion.
Kairoz supposedly had this idea on his own, but given his allies (sadly not seen in-game. I would have loved to see Infinite Dragons doing stuff on Draenor) and even his choice of words (he claims that he would become Infinite just before Garrosh kills him) it really seems like this is part of something larger.
So what if, then, the Infinite Dragonflight is not the Bronze flight's future? What if, instead, the Infinite Dragonflight is actually something very similar to what Kairoz planned, only rather than Orcs, Murozond goes around recruiting dragons?
Nozdormu believes that the vision he received from Aman'thul was meant to humble him - to remind him of his own mortality. But what if the real message was "this is your enemy."
Without the ability to look throughout all of time - an ability that the Bronze Dragons lost when they poured their power into the Dragon Soul to kill Deathwing - we have no way of knowing just how far the damage wrought by the Infinites extends. Our greatest victory against them has been killing their leader presumably after a very long life of doing exactly what he planned, and in a future that either no longer exists or is part of a separate universe from our own.
We have our Bronze Aspect now de-powered and resigned to a fate of corruption and eventual death.
And for all the damage they have done, the Infinite Dragonflight has literally not even started.