I've watched the movie on TV since I was a small child in the early 70s, and I don't remember a scene like that after the melting.
There was an extra dance number, "The Jitterbug" which was cut from the film, but that scene has turned up on DVDs as a special feature.
The original audio recording exists of "Hail, Hail the Witch is Dead", it is the actual missing video footage that is in question.
I thought it was "Ding Dong The Witch is Dead. and I remember that scene too.