Not sure where to post bug reports. That said, I was checking out the Dragon Priest masks as a result of reading another post about a wooden mask. I went back to my chest where I save unique items and found that Volsung was missing. Upon returning to Volskygge and checking his coffin he was still there, he had never emerged to fight. I finally got him to rise by casting "Revenant" on him and subsequently killed him and got the mask.

It should be noted that I had cleared this site prior to loading the unofficial patch and this may have resolved the issue. If not, then heads up...

http://www.gamesas.com/forum/179-skyrim-hardware-and-software-issues-subforums/.