I remember well, seeing the MM Vanish and how Peter and I both nearly cried it was so elegant; it was as if the girl raises up off the floor and simple dematerializes.
I do believe there is footage of Merlin, quite a bit of it. But the Henning estate has kept is "sealed" for lack of a better term. I don't recall all of the scuttlebutt around it, but as I remember things Doug simply didn't want to share something with the world that was but a pale shadow of the actual production... video just don't do it justice and knowing how certain effects, such as the floating sphere in the opening felt from being in the audience, I can more than understand Doug's position with things.
this has been a very emotionally driven few days when it comes to memories of the past. Been collecting stories about Kirkham of late, in hopes of composing a Biographical on him and his amazing life within magic and the movies. Who knows, I might even tackle the life & times of Peter Pit after that, he was one of the other major influences in my early adult years