I am pretty sure that even when WoW ends, we will not be killing sargeras. The warcraft brand is too expensive for the "master evil" to get killed. Plus if it were true, we would probably kill him at the end of the game's life when a lot less people are playing. They probably wont destroy their (half a billion dollar worth?) brand for that small amount of people. It is much more profitable to have a WoW 2 in 10+ years from now. Just from name recognition alone it will sell huge amounts.
Maybe we will kill all the old gods and in some way still get to keep the earth by titan intervention. Then WoW 2 or an RTS can start a 1000 years from now where there has been peace across azeroth, history has become legend yadayadayada untill one goblin finds a helmet on top of what looks like a man made mountain in a forgotten frozen continent up north. And at the same time a rift has appeared in the eastern kingdoms, voice appear, they whisper the word Sargeras which nobody can understand.....DUN DUN DUN.
Anyways, a new era of Azeroth with new lore. Something like that. They do need to go out with a bang though so perhaps the old gods will get killed.
IF we are truly talking about ending wow than in my view there is only one true end-boss: ME (meaning the player).
I imagine that I (as hero of azeroth) grew too much in power and all faction-leaders want to get rid of me, because that much power in one person is just too much.
So I will be drawn into an instance and all faction-leaders will attack me; I am the final end-boss of wow.
I really can't imagine a more epic ending of me through Azeroth, growing in power, defeating evil... I the end I became the biggest threat.
They should go alllll out on the final raid. Make it the size of a zone, 30+ bosses and make heroic mode teeth grindingly hard. I assume the final boss would be Sargeras or for some twist of fate, Aman'thul.
That sounds awesome, to be honest.
Cue post-apocalyptic WoW expansion after that.(titan?)
I took some time to write that, because even if it would be awesome, i'm sure we won't kill Sargeras, and so i had to think about something as epic. Glad you liked it (:
And that would allow Blizzard to start over with another plot after the apocalypse, of course!