I'm glad you liked the story. Well, I'm sure Blue would be glad. All credit goes to her, obviously.
The adventurer who founded the Last Mug is never named, leaving the player to wonder whether Indigo is being modest, or whether the origin is lost to time (unlikely, as Indigo looks like an Elf).
Upon inspection, Indigo actually looks to be a half-elf. However, I think it works well to leave the founder unnamed. My reading is indeed that it was Indigo, but I think this is better left up to inferrence, unless there's a particular weakness in leaving her unnamed.
Indigo is obviously familiar with the Last Mug and apparently knows a way out of the Underdark (she does not indicate that her escape was by magical or similar means), yet makes no mention of helping others back topside, or marking a path, or anything. One would think that a person who so obviously sympathizes with the plight of surfacers trapped in the Underdark would do her damnedest to try to save them--and if that means joining the PC's party to direct them on a rescue mission, so be it.
There's something very abstract about the Last Mug as it is, and I think that's something that'd be lost if it was anything more than a surreal tale for consideration. One original suggestion I received was to actually have the player trapped there at some point during the Underdark, but I didn't feel I'd be able to pull this off without it looking stupid (or at any rate, pull it off as effectively as Blue's tale works). On top of that, it doesn't seem to me that returning to the Underdark would be something Indigo would be likely to do; while she may feel their plight, she seems utterly without hope.
And of course, there's me not really wanting to commit to making a joinable NPC.
"Take this, and share a final toast with me-" Take what? Her advice of "Do not return there?" If a physical object was supposed to change hands here, I must report that none did so. The conversation should provide a small amount of EXP--the listeners, do, after all, learn something.
It's the advice, rather than a physical object. I've added "for contemplation". And yes, you're right about the XP. The tale now grants 5000, which seems enough for a chapter 6 party doing nothing at all.