Quest items and boss monsters are randomly placed on the third level of one of the dungeons. Since you have cleared all 6 dungeons, he appears to be missing due to a bug or glitch.
Raze might not: but I would certainly suggest that you revist all the lowest levels again - sometimes the quest monsters are not all that obvious (that is they do not show up as a 'red dot' on the mini-map until you are quite close).