An aunt of mine in her late 80s, with fairly advanced dementia was refusing food and drink after the umpteenth UTI - she’d always been prone to them so of course dementia-related incontinence made them that much more likely.
The care home staff asked me whether I (the only relative contactable at the time) wanted her taken to hospital for IV fluids/ABs, or left where she was, with palliative care, but where she would otherwise die.
It was a horrible decision - I could only ask the GP what he’d do if it were his much-loved aunt. He said that especially since it was only going to happen again, probably quite soon, and since hospital is a terrible place for anyone with dementia (when they can’t understand what is going on or why) he’d leave her where she was, where they’d keep her comfortable.
I sat with her a lot during her last days - she was sleeping nearly all the time and did not seem to be in any discomfort. Staff continued to offer drinks and e,g, yoghurt, but she’d close her mouth and turn her head away. Her mouth was kept moist with little sponges.
She drifted away quite peacefully after about a week. Although it was a horrible decision at the time, I never once regretted it afterwards - I was quite sure that it was what her former self would have wanted.