I loved the scene the only time I did it as well! I actually used a good ol' Scroll of Icarian Flight to jump on his throne, then launched a single Black Dart at him. I watched his guards and him panicking, running around down there and helplessly watching their King meeting his slow but inevitable death... You see, none in that room had any ranged weapons or magic to reach me when I was up there on the throne!
Got down there, looted Helseth and teleported the heck out of the room.
I've gone back there a few times after that to openly meet the dyed-in-the-wool outraged guards in combat. I've sliced one or two of them each time before the rest had forced me to retreat from the room. They hit hard! One of these days I should check if anyone's still alive in there; I can't remember.
I believe no-one actually reported my crime or anything. o_O Only that everyone in that room (understandably) hate my guts nowadays!