Thirst and hunger. They’re meant to die a peaceful death so pretty sure no predators involved.

Go to a dementia facility and hang out with your those people. You will see suffering.

My grandmother died of dementia.

If you think that "cannot feed themselves" is when a person is already completely gone and it's okay to "leave them under a tree to die of hunger and thirst", I've got news for you.

My mother has dementia, so maybe dementia just has different expressions and you shouldn’t generalise ?