Originally Posted by
Qualia
I thought so for a while too, especially given that he was always stuck at 1HP at the end of the fight for my guild in the Nether. However, at Blizzcon, Blizzard said that the original idea was that Archimonde died there and would be "dead dead for good", just that it didn't come across well enough in game. So current canon is Archimonde's dead. However, Kosak also stated that "*MAYBE* we will change that. Maybe we'll change the canon of that, but that's the idea we were working with", so well - maybe he isn't dead after all.
Still, for now, it's canon that Archimonde is dead. We don't know if they changed that. We don't even know if Kosak's "that" (in his "Maybe we will change that") was referring to Archimonde's status, or the fact that it didn't come across well in game for that matter. Although, Gul'dan called the player character "slayer of Archimonde" if you have Mythic achievement - that seem to indicate that Archimonde is indeed dead.