Well, in fact my players did die on the "Isle of the Ape". (Lost to madness & imprisonment in the "Spheres of Thought", actually.)
Here's a follow-up to my follow-up question, now that I'm cogitating about this adventure. I'm not sure if you actually ever ran it in its published configuration (search for the Crook of Rao), but when I ran it I did wonder about the following:
- How did you ever deal with the initial combat with some ~300 barbarians of varying high levels in AD&D? (Personally, I had to jury-rig a set of mass-combat rules to handle it.)
- What was your expectation for how PCs would succeed at the adventure? (My players never got any clues about the 3-part ritual, and to my surprise were led by the map handout directly to the "Spheres of Thought" after battling the initial natives.)