I think if I was going to fire that off as a death curse I would simply curse the cleric to wander the world until he had learned "the Truth." That way you avoid the ever expanding knowledge base of mankind and get to force the character to never know if what he has learned is the final truth or if something he has already learned is simply incorrect so he has to constantly reexamine everything he knows as well. Also I like tossing in the wander there so he never has a chance to set up shop and really become a danger to anyone.

Gotta say had I been that cleric who recieved the curse posted by Harlan Quinn I would have one of my followers dig up a dozen or so mathmatical formulas or other facts and seal them up, far away from me. I doubt I would spend much time in the quest for knowledge in this case since I could use my new immortality to hunt evil for all time.