No, a person with memory issues is not dependent on any single person's body for survival. They are dependent upon any person who offers to put in the work, and that person can quit the job at any time without penalty. Someone else will replace them quite easily.

We don't put slaves in charge of the care for the mentally handicapped. A woman who wants to be a mother does so voluntarily. But if you force a woman to keep a baby when she doesn't want to, you are forcing her to labor. You are making her a slave. And lethal force to escape slavery is always self defense.

That's why the example you gave is bad and irrelevant