You know, I completely disregard the 'one Legion all realities'. To me, this doesn't exist. Up until now, ignoring it hasn't created any lore flaws, so I'm going with it. If any problems arise, I'll try to explain my way past them.
Thus, Archimonde dies physically at Hyjal and later reformed in the Twisting Nether because he is a demon. We haven't heard from him since. The one in WoD is a completely separately version of him, who never got to see Hyjal again.
As for Garrosh, absolutely! I will also probably note the difference between "city orcs" of Orgrimmar, Razor Hill, etc. and "rural orcs" of the Barrens and such. I don't know how exactly I'll be going with this, but you can count that I'll include it.
I didn't really understand your comment on Arthas. Did you mean Icecrown Citadel instead of Light's Hope? If so, I do believe that Arthas had the upper hand, and eventually went all "APOCALYPSE" on us, and utterly killed us all, except for Tirion. The Miracle freed him, stunning the Lich King and allowing Ashbringer to shatter Frostmourne, thus releasing the souls within, including Terenas, who proceeded to resurrect (in one of the few instances in canon lore where someone's is actually resurrected) the players.
But remember, I don't change the story in any way - I rather interpret it in a realistic manner, so Garrosh will still be besieged in Orgrimmar, N'Zoth still won't be free, etc. The truth is, while such changes might have made the story better, they are still only imaginary. I prefer rather to take what we have and make it awesome
Anyway, any specific comments or anything that might have caught your attention?
As for the end of WotLK, I'll be getting there pretty soon if I have enough time xD
Okay, as you might have seen, my interpretation of canon involves a lot of loss and failure, as well as the heroic victories we're accustomed to. Events happen for a reason and they have consequences.
I also dislike having strong figures simply fail before us, as you may have seen with Kil'Jaeden's plan on partially coming through the Sunwell with the main purpose of rousing the Lich King, thus having at least a partial victory. For the Lich King's fall, I will probably focus on his plan to get the champions of Azeroth to the Frozen Throne only to kill them and turn them into death knights. I will also talk about how that 'Miracle of the Light' might have been the single most crucial moment in history, and may have more behind it (Xe'ra?).