This has been a confusing thing for me since BC came out... Are the prior expansions dungeons, raids, quests, etc. done in lore?
Is Hakkar dead, is Ragnaros banished, Onyxia killed, Dead Mines cleared.. These are all really important things, but it seems like a lot of people (including myself) are unsure about where they stand in lore. Short post for a really important topic
According to Wowwiki and blizzard lore, yes. Ragnaros however is being brought back to full power. Now what I can't anwser for you is...if this is the case on CotH. They may or may not be alive here.
Hakkar is not killed, I know that much.
And I think I remember this dicussion when I first came here with the conclusion that the only bosses that have died here on CotH is Kael'thas twice.
The only intelligent realisation is that all the bosses up to Northrend HAVE been defeated.
It's like going into Star Wars, except EVERY SINGLE BAD GUY (Regardless of the timeline) IN THE ENTIRE UNIVERSE is alive at the same time and trying to kill you. Dark Malak and Boba Fett trying to kill you at the same time.
WoW is a linear story, it goes along one path. The chronology of the dungeons are according to level and patch number, so you can SAFELY say that Onyxia, Kael'Thas, Hakker (Not dead, but corpereal form defeated), C'Thun and all the vanilla/TBC bad guys are in shallow graves.
Anything else would be folly.
I'd say most of the old "villains" are dead, but in some cases it could be bent to create a storyline, but it depends entirely on which character and how the storyline is presented.