Old age was a common one, so powerful magnates might pass the mantle to their heirs and retire to a monastery to spend their last years atoning for the sins that they commited to reach and stay at the top of the ladder.
I have written and run a mini adventure that deals exactly with that: flambeau got a bad twilight, comes back god-bothered, goes on the 4th crusade to absolve himself of his sins, boosts his finesse and CrTe to create a (flamboyant gothic) church and takes to being just an old brother tending to it: refusing to use his magic again Book raid on Katsberg (a short 2 hr adventure)