In my experience as a doctor, people spend too much time thinking about uncommon scenarios and not enough time talking to their eventual decision makers (usually their kids.)
The final scenarios are almost never what people address in their advanced directives e.g. “being kept alive by a machine” or locked-in syndrome. The real dilemmas are more like this: Dad keeps getting pneumonia because he aspirates because he can’t swallow normally anymore since his stroke. Or Mom lives in memory care and 3 times in the last year she’s been hospitalized for urosepsis (UTI that went to her blood) and these hospitalizations are absolutely miserable for her because she gets delirious and she falls out of bed, and on and on.
So I’ve talked to my kids at length. They know that if I’m old, weak and my memory is going that I want to be comfort care only. No hospitalizations, no antibiotics. Pneumonia is sometimes called Old Man’s Friend. My kids joke it’s a #LifeGoal of mine to die of an infection, and it’s their job to make sure I’m not blocked from attaining my goal.