From what I've been hearing, it seems to go like this.
There's a Bell. Garrosh wants the Bell. What a sissy.
The Bell seems to be taken to Darnassus for safekeeping (not positive on this part). Garrosh conscripts the Sunreavers into providing the Horde some portals between Dalaran and Darnassus, slipping under the Alliance's (and Jaina's) shields and barriers. The Horde takes the Bell... and Jaina realizes this was an inside job and heads back to Dalaran pissed to high hell.
Realizing the Sunreaver's involvement, she imprisons their leaders in the Violet Hold and kicks out all of those who surrender. Angered by this action, the leader of the Blood Elves (Lor'Themar Theron) sends the Horde in to rescue the captured Blood Elves. While successful, this convinces Jaina of the Horde's guilt, and she declares Dalaran for the Alliance exclusively once more. Lor'Themar realizes too late what Garrosh has done, and how he's as bad as the Alliance of old. He ends up muttering something about reforging old alliances.
Meanwhile, Garrosh's Bell is obviously bad juju. Andiun tells him as much, but Garrosh likely doesn't care. Anduin gets himself killed (probably while trying to stop whatever apocalyptic Sha the Bell unleashes).
But now we know the set up for everyone killing the ***k ****e* ***h**less *** (I really hate Garrosh) of an Orc we have had to deal with. I can't bring myself to listen to any of it.
Despite the sound files, I don't think Anduin stays dead (or actually died, perhaps). 5.2 is unofficially called "The Two Princes" based on the Wrathion legendary quest chain. Wrathion is referred to as "The Black Prince;" Anduin is the "White Pawn." Both want to see the war stopped. My guess is that if Anduin does die, he gets resurrected by the healing waters found in Pandaria.
Also, I'm still scratching my head about Lor'Thermar Theron's "old alliances" comment. He just got finished trashing the Alliance as being the reason for the Horde, and the Horde under Garrosh for being as bad as the humans. Who does that leave for allies? Naga? Broken? High Elves (unlikely, given the events transpiring in Dalaran)? Draenei, as they worked together in the Sunwell Plateau?
Also, some of the new scenarios sound awesome. Varian's Trials of the High King are coming up most likely; Horde will have a scenario with Thrall from what I've read, and Warlocks get a legendary quest scenario that goes into Black Temple and retrieves the first artifact-quality item in the game.
One more bit of musing: Ancient Teleport: Dalaran would make a lot more sense if some of the changes that are being talked about happen. Currently it just deposits you above the crater of Dalaran, where you plummet to your death (or slow fall, or ice block). While funny and somewhat useful, the spell is relatively recent and makes a lot more sense if certain changes come to pass...
New sound files out, including some for Varian, Jaina, Vol'Jin, and some scenarios. I haven't listened to them all, but the few I did hear revealed: Anduin does NOT seem to die, but it critically injured by Garrosh. Varian was in negotiations to bring the sin'dorei back into the Alliance, but Jaina's actions in Dalaran busted that up and sent them back to the Horde. Vol'jin is PISSED at Garrosh, because apparently Garrosh is using "da blackest of magic" to make Saurok. Every time I hear Vol'Jin talk, I think of Sebastian from "The Little Mermaid."