Funny thing that. The question did indeed come up, last week when I was at the doctor's (and later the hospital) with suspected angina (false alarm). I did mutter to the doctor something like 'worst possibly thing you could say to me at this moment, tell me to lay off the bike'. He reassured me: 'no, no chance of that, our aim will always be to get you back on the bike ASAP'.
But of course for some people there's no option. My father-in-law simply found he no longer had the strength, nor the sense of balance, after suffering a stroke. But he did invest in a battery-assisted trike. It gave him some measure of independence for his few remaining years - and he wasn't bound to his car.