How is the party supposed to get out of Gromph's Inner Sanctum in Out of the Abyss?

Question

Warning, spoilers for Out of the Abyss below.

In Out of the Abyss, Gromph's Outer Sanctum and Inner Sanctum are described on pages 206-207. On page 207 specifically, it describes this methods of getting from the Outer Sanctum to the Inner Sanctum:

Opening the secret door requires a knock spell or a successful DC 20 Intelligence (Arcana) check to assess and manipulate its magic. Beyond it lies a dark void that can't he dispelled or destroyed. Anyone or anything that touches the void is instantly transported to a labyrinthine demiplane similar to that created by a maze spell. A creature that succeeds on the DC 20 intelligence check to escape the maze reappears in the middle of the outer sanctum. However, if a creature casts a spell of 5th level or higher while in the demiplane, all creatures and objects in the demiplane instantly appear in Gromph's inner sanctum instead.

So after everyone got stuck in the labyrinthine demiplane (they all failed the save), the party cleric decided to cast find the path (a 6th level spell), hoping that it would lead him out. Since it triggers the "5th level or higher" spell condition, it worked, and they all ended up in the Inner Sanctum.

How would they get out? The only exit, as described in the "read out loud" description box on page 207:

The only exit appears to he an archway filled with a black void.

They can't use any form of teleportation because of this (p. 191):

Shielded City. The drow have locked down their city in the wake of Demogorgon's rampage. For the duration of this adventure, creatures can't teleport into or out of Menzoberranzan. [...]

At the time, I ruled that they could all just jump back into the void, then use find the path (any 5th level or higher spell would have done it, but this is how the party understood their previous success) to get back to the Outer Sanctum. However, a strict reading would imply that this would just dump them back into the Inner Sanctum again.

What is the "real" way the adventure expects you to get back to the Outer Sanctum? Would everyone really be expected to succeed a DC 20 Intelligence save? Even characters like dumb barbarians that can't succeed that save (as it happens, the party barbarian doesn't have a -ve Intelligence modifier, but he could have been a dumb barbarian; Intelligence is a popular dump stat); or is there another way to leave the Inner Sanctum that I'm not remembering? Or, is the way I handled it in fact the correct way, and my "strict reading" is incorrect?

Answer 1

The way out of the inner sanctum, as written, is merely to re-enter the demiplane through the black void, and then make a DC 20 intelligence check to exit to the Outer Sanctum.

Very importantly, this DC20 Intelligence check may be made every turn until it is successful.

A character with an 9 or less intelligence score (at least a -1 modifier) could indeed end up stuck forever, if they're alone.
But presumably they're not, and the party could assist them in escaping through:

1. Guidance or bless
2. Bardic Inspiration
3. Being carried out in the possessions of a smarter creature
4. Teleporting, but remaining inside Menzoberranzan
5. Passing them a Headband of Intellect
6. Kill them, cut a hand off to take with, and Resurrect them outside.

And of course DM Fiat (what you did) which is an expected solution in 5e to problems that don't have specific solutions presented in the text.