hehehe I don't think aabby757 was asking about DCI....

(yes it was 88 and 89...but I believe the bit with the entire corps disappearing was 89 only.)
Anyway, as far as the Broadway show is concerned, according to one guy who has seen the show many, many times, he says this about the chair: "It has a false back. When the Phantom throws his cloak over himself, he attaches the top to wire which pulls out, keeping the shape of a head. The back is released and he can move into the false back of the chair. If Meg sat on the chair at the end, she would be almost sitting on the Phantom's lap."
I myself have seen the Phantom show on Broadway. Unfortunately that was many years ago and I don't recall exactly how the final disappearing bit looked. However, having worked in theatre for many years, this explanation sounds about right.
Hope this helps!
.....Kelly
FYI - Stan, I graduated from Madison HS in 1995. From 92-95 our drama department, Madison Theatre Arts Guild, was the bain of SDSCPA for we had one of the strongest theatre programs in the district. On the whole, your school and mine would jointly sweep most of the theatre competition awards.