Alzheimers and when to step in

My grandmother's youngest sister (late 80's) wandered away from home late last week. She has alzheimers and although she lives with her husband, he also has physical issues so taking care of her is hard.

She was finally found outside of a family's garage in the neighborhood. She was missing her glasses and was bloody from head to toe. Nobody knows what happened to her. She's in the hospital and arrangements are being made to move her to an adult living facility.

My mom and I were talking about this and really started wondering when children should step in. Certainly, had anyone known it would have gotten this bad, family would have stepped in earlier, but it's hard to predict the future. I know the older adults in our family do not want to leave their homes and move into any type of care facility. We are independent and sometimes cranky about it - LOL........ However, we do tend to live pretty old - both my grandmothers are still living and they are in their 90's. So the question has to be raised.

So - how do we know when it's time to step in and take over for our parents and grandparents without taking away their dignity? I don't know that there's a truly good answer.