So I went to the Shrine of Peytite a while back and Kesh was annoying me so I killed him. Can I still start the quest The Only Cure? Or will I never be able to obtain that daedric artifact?
This article on the Elder Scrolls Wiki would suggest that it is possible to complete the quest even after killing Kesh. Depending on what part of the quest you are on, there seem to be a few different options on how to proceed. I haven't gotten to this particular quest yet, so I can't personally confirm what's being said in the article.