Most of the oldest people in the past have been nobles, how did the people under the nobles deal with a Lord suffering from dementia? Did they just ignore it? Did they actually try to fullfil whatever weird wish he must've put forward?
Edit: Particularly in the medieval times
On /r/AskHistorians, you might get a better response if you specify a particular time-period - were you thinking, for example, of what would happen in the medieval era?