SilverWook said:

IIRC, on the "Rock and Rule" DVD, a vault fire was mentioned as to why the alternate cut of that film survives only on videotape.

I have to wonder what else Nelvana may have lost?

That would be unfortunate. But then how did Lucasfilm get hold of the Leica animatic reel, and why didn't they have the cartoon as well?

It begs the question of where the original film reel would have resided. What form did CBS receive it in, in 1978? Was it already converted to videotape? If so, that might explain the source of the alternate cut floating around. If not, and CBS got the cartoon on film, they would have had to telecine it themselves and insert it into the HS...and then where did the film go? If CBS hung onto it, Lucasfilm would have picked it up when they acquired the HS rights and masters in the 80s. If they sent it back to Nelvana (which seems unlikely), then it could have been lost in that fire.

Did the "Rock and Rule" DVD specifically mention the HS cartoon being in the fire?

--SKot