The youtube video can be found here.
Some points of note…
- This video documents the session after you defeated the Arch-Priestess Bloppblippoodd.
- The action picks back up around 6:50.
- The rise of Demogorgon starts at 11:00.
- Ront dies at 14:00.
- Lancel, Ralxus, Elanelis and Erdan go catatonic at 15:30.
- Varis and Blanton start their escape, dragging the rest of the companions along, at 18:30.
Here is the link to the Map of the Underdark.