Both my mother and my FiL had dementia, both eventually had to go into care homes (funded by themselves) once they needed 24/7 care. My mother had dementia for about 15 years and went on to 97, in a most pitiful state for the last few years, doubly incontinent, not knowing any of her family, unable to hold any sort of conversation, etc.
After that experience, I have made a Living Will to state that if I ever get dementia, or any other condition where I am unable both to care for myself and speak for myself, I emphatically do not want any medical interventions to keep me alive just because it is possible to do so, when Nature might be trying to let me go.
From all I've seen and heard over many years, there is far too much keeping alive of people who are both very elderly and have a very poor quality of life. People are stuffed with medication, in and out of hospital on drips, coaxed and badgered to eat and drink when they no longer want to do so,
prescribed endless fortified drinks to keep them going because they can't or won't eat enough.
For what??
By the time my mother was in later stages and no longer getting any enjoyment out of life, we made it clear that with the exception of anything like fractures, there was to be no hospital - in any case a pretty awful place for anyone with dementia - and no interference if nature might be trying to let her go. Quite apart from any other consideration, we knew it was what she'd have wanted for herself.
With an aunt in a similar condition, when the situation did arise (hospital or let Nature take its course?) we were asked to choose. Of course it's never an easy decision, and I could only ask the GP what he'd do if it were his much loved aunt. He said he'd leave her in the care home, in familiar surroundings, where they'd keep her comfortable.
But I have heard of so many cases where relatives are insistent on keeping someone going, no matter how pitiful the state they're in, and are very angry and indignant if anyone suggests it might be kinder to let Nature take its course.