Issues with the previous TPK(nockout) aside, where do we go from here?

The party is unprepared for the ultimate battle and they have boxed themselves into a dungeon with only one exit, where they face two, possibly three foes, (if MitD shows up,) any one of whom could defeat the party on a good day.

It is far too early in the book for Xykon to loose, unless he's been the McGuffin all along, (contrary to Mr.Burlews statements on the subject.)

So, the party can force Xykon to retreat, possibly opening up an opportunity to visit the Astral Fortress, or the party can lose, with nowhere to hide.

This leaves intervention by Green and the paladins. Green seems like the kind to watch things unfold rather than directly interfere, so I assume her help will come after the fact.

Also, Xykon's thing with coffee forshadows Belkar's inability to savor his next birthday cake.
(that last bit is a joke, just in case you didn't know)