Ok, so call me a nerd, but I had a pretty sweet idea.
Was just walking to the store listening to The Day The World Went Away by Nine Inch Nails and got to thinking.
This song is perfect for Cataclysm!
For the beginning of the song I visioned Garrosh talking to Magatha about taking out Cairne, NPC's in towns doing their usual stuff, enemy/neutral mobs going about their daily routine as well. Then when the song begins to fade, Garrosh and 2 other guards begin to walk slowly over to Cairne, switches over to some NPC's in Orgrimmar looking towards the front gates as it's set ablaze.
Anyone remember that little female Orc in Northern Barrens, at that farm who's chasing the bugs? I pictures her continuing on, but as a large shadow fell over everything in site. The Dad (or whoever it is in the house) begins to walk out and looks up in horror.
Then the songs kicks back in.
Garrosh's guards assassinate Cairne. Mobs of enemies pour into Orgrimmar as guards and civilians begin to panic. A giant wave of water engulfs the Dad, the little girl, and the farm. It cuts to Crossroads as NPC's are knocked down from the earth cracking and fire shoots up from the cracks.
That's about as far as I thought into it.
I'm dumb. lol