I guess I got lucky and happened upon a great tactic for defeating the dragon.
I sent my rogue (main char) to start the encounter and chose the most aggressive path so there wasn't a lot of talk. (didn't know about the scale breaker skill). Following the conversation, I entered stealth and was able to withdraw without combat starting.
I then decided to explore the area and followed the path down and around towards the treasure room. That's when I ran into the Xaurips and decided that I should take them out first and THEN deal with the dragon. Using stealth, I was able to manuever my entire party along that route and started engaging the high priests first. Things were going great until I saw the dragon coming in from behind.
I immediately broke all contact and moved further into the treasure tunnel, leaving some of the xaurips behind, thinking they might block the dragon, which they did long enough for me to finish off most of the adds including the Adragan.
I then started kiting the dragon using Kana's summoned wurms for a barrier and just ranged the dragon with all characters. That wasn't to effective due to the defense, so I threw down a wall of force and between the hobbling and the crushing, it made a HUGE difference and the dragon's health started dropping steadily. Wall of flame did a nice job of chewing up the dragon's health too.
Rinse repeat. Piece of cake.
A few times I used party summons like the beetle and through some heals on it while Kana's chant recharged. The wall of force just stops the dragon cold due to the hobbling effect.
Oh yeah. Did this at 9th level on Hard and didn't lose a single person.
