I had a problem with a very old ruler. As Byz I was walking towards victory. Had a few heirs but everyone was getting older and older. 5 royal princes over 55. Ruler aged 76. Two turns later I had lost.

Ruler died of illness. No princes left -others turned to generals, others must have been brothers of original king. Next turn new king dies of illness. Agh!!!! 20 hours of play up in smoke! I never reload save games (I feel it is sorta cheating).