My own dear departed father was totally cowed by my mother and her demanding ways and orders to "do this" and "don't do that". The older he got the quieter he got, until it got to the point where he would just sit there in his chair staring at the TV, ignoring her.
He was in his mid 80's when he died suddenly of a heart attack one day. Mom, rather than mourning the loss of her spouse of 60 some years, became very angry. Angry that he had "left her here all by herself' and "now she had no one to take her to the store". (She hadn't driven for some 5 years prior to his death)
There was a time about two years prior to his death that Mom fell and broke her arm in three places, as it turns out. She refused to allow him to call an ambulance, insisted that he "drive her to the doctor's office", which he did. They of course, promptly got her to the E.R.
But I know that if Mom said "No ambulance" he would not have dared to call one. He was just too old and too tired to fight her - not that he ever did much anyways.
So what goes on in the dynamics of these oldsters when the dementia sets in can result in situations like this one, I am sure.
By the way, just for the record, there are other forms of dementia than Alzheimers. There is senile dementia and there is vascular dementia, to name just two others.