I was thinking about the kind of stuff that's going to happen as far as the NPC's like Tirion and Darion during ICC. This is what emerged:
The fight starts off with the raid engaging Arthas on the Frozen Throne platform. Varian and Saurfang the Elder are there from the start, aiding the adventurers with Stormwind and Krok'ron (spelling?) guards. The Skybreaker (or Orgrim's Hammer for Horde) will be circling the throne occasionally shooting cannons onto the battle.
At about 80%, the Lich King will summon waves of some sort of adds, but instead of being dealt with by the heroes, Darion Morgraine and the Knights of the Ebon Blade (Thassarian/Koltira as well) will enter the fray, dealing with the adds.
The same will happen at 60%, but with more adds and Tirion, Argent Crusade knights and possibly Palatress/Eadric joining too. Both of the groups will be on one of the detachable platforms, packed tightly together.
At 50%, the waves of NPC-fought adds will stop coming and Tirion and Darion will rase the flag of the Ashen Verdict, and charge Arthas. All cooldowns must be blown now, and the raid MUST get him to 10% within three minutes of this frenzy, where he will become unattackable. Adds will arrive and need to be off-tanked, and this time the NPC's won't deal with them. Also during this phase, you can hear Muradin yelling from the airship that they are under siege by Valkyr or some dangerous sort of Scourge. The airship is out of control and heading towards the Throne....
At 10% or the three minute timer, whichever comes first, Arthas will become unattackable, and knock back all the NPC's and players towards one side of the Throne, where it will begin to crack. 2 seconds later, the part of the Throne will crumble and fall off. Tirion, Darion, Saurfang, and Varian will manage to hold on, while other Crusaders and Knights will fall into oblivion. The NPC's are hanging on to the side of the platform by one hand, dangling out over the edge. The raiders are stunned wherever they ended up when the platform fell off.
Arthas approaches Tirion and gives a little gloating speech, stepping on the hand of the paladin and Darion while talking to Morgraine about his potential. Suddenly, an apparition of Darion's father, Alexandros Morgraine appears, stunning Arthas and knocking him back to the center of the platform, where he grows infuriated and starts channelling an apocalyptic spell, while Alexandros' ghost fades away. While this is happening, Bolivar (aka Lavaman) dashes into the room and pulls Tirion up from the edge before dying due to his severe burns.
At this point, the Airship will crash into the other side of the throne, removing the raiders' stun and forcing them to move from that part before it falls off. The Lich King is jarred and drops Frostmourne. Darion picks it up, prevented from the soul-stealing by the essence of his father. Arthas is still yelling about how he will kill us all. Then, Tirion and Darion strike Arthas simultaneously with Frostmourne and the Ashbringer, bringing him down to 45,000 health. At this point, the players' stun will be removed, and they will strike down Arthas.
Hooray! Phat Epix for everywun!