What causes people to die from Alzheimer's disease?

Usually something physical/medical. My mom's lost a great deal of weight because food tastes different now. Shut down of organs, pneumonia, etc. is usually what happens.

people die from complications of alzheimers disease not the disease as such... Many elders have multiple diagnosis's so it is often hard to know.

From what I've heard, the person doesn't die of Alzheimer's Disease (AD).
It's usually something else, e.g. pneumonia.
Hope this sheds some light.