I happened upon the wall where Krosis is (about level 42) and started fighting the Blood Dragon that was with him. My character is a mage and powerful against most opponents, but dragons are a bit... difficult. anyway a couple of minutes into the fight a Revered Dragon showed up to join the fray, and fighting the two dragons and Krosis got very hectic.
I conjured a spectral sabrecat and he immediately went after Krosis, leaving me to deal with the dragons. I saw them heading along the upper hillside that leads towards Valthiem, but then my attention was distracted by the revered dragon. That's the last time I saw the sabrecat or Krosis.
After the dragons were dead, I went searching for Krosis, and after spending the entire day hunting I found nothing but a dead wolf. Then, completely unexpected, two MORE dragons attacked (no sign of the three day waiting period eh?) one was a spectral dragon who spent half the time invisible, and who could also split and become 2 dragons (listed respectively as "Spectral Dragon" and "Spectral Ally". The other dragon was an Elder Dragon.
I have now spent three days game time fighting these two, and I don't believe I can kill them. They are almost as healthy now as when they first appeared. I would simply slip away, but I still want to search for Krosis, and they are making that impossible. I've never completed gathering all of the priest-king masks, you see. That makes this an important issue.
So, if I were to manage to kill these dragons (not looking so good currently), what if Krosis fell through a rock or something? Other than by console command and adding the mask, can anybody think of a way to find his body (or ashpile)? Also, I have no evidence that Krosis is actually dead, other than wandering around his area for four days or so now without encountering him...