It's hard to believe the son didn't talk to anyone about his mother's condition. I don't care if he had a slight developmental disability or not. Simply uncounscionable.
My stepmother (and her two siblings - all in their '60's) had to deal with THEIR parents - from their parents' 80's into their 90's. Their parents fought tooth and nail against going into nursing homes, assisted living, you name it, although they no longer could really get along by themselves, and weren't very ambulatory to boot.
After at least a year's discussion, they finally got a health caretaker to take care of the parents during the week. During the weekend, the siblings had to rotate weekends and take care of these creeps themselves. (Prior to this my stepmom had taken care of these ungrateful jerks for 7 frigging years before marrying my dad - the only words her parents asked her when she gave notice was, "What's going to happen to us???") Kids aren't the only ones who are ungrateful assholes.
Her parents finally died within a year of each other. They both died at home. My stepmom is too much of a lady to say she's relieved, so I'll say it for her.
I think when parents become senile or unable to care for themselves (and hey, aging happens to all of us), other people need to intervene.
I believe that by the time I hit my 90's euthanasia is going to be public policy, so I'm not worried about non-existent kids taking care of me.