Maybe you could restrict the area with NPC_noentry (or what was the special clip shader again) and use camera_groups for the NPCs to keep them on the center of the view. Then just turn them loose and let the AI do the fighting, at least as far as you would like something special to happen. And you could of course just put there triggers that only control the cameras. That way you could also keep the action close to the view.
You could monitor healt or just let the fighting go on for some specified time, and when that happens, turn them to behaviorstate(cinematic) once again and make them go to some specific spot, and continue with more traditional fully scripted cinematic work.
Frozen by ICARUS