My Moms DC said heart failure. I don't agree that Dementia is not fatal. If Mom hadn't had it, she may still be here. When Dementia gets to the part of the brain that controls the heart and breathing and thst part dies, so do you. My Mom otherwise, was healthy.
It's tricky because permanent heart failure always goes with death, and it has been used as a carpet-bag term when causation is tricky or embarrassing. Perhaps not in your mother's case, but sometimes the question is what caused the heart failure!
Yes, when my Mom died it was just her body shutting down. They never had an actual diagnosis to be honest. Dementia was a symptom of getting old, not what ultimately ended her life.
So to answer your question, there could be a number of ways a person with Dementia dies, diabetes, heart problems, cancer, the list goes on and on. Dementia could cause a person to not handle their declining health correctly and so could be considered a contributing factor in their death. But not the ultimate cause.
What does the Death Certificate say? My understanding is that dementia is not necessarily fatal in itself. 'Heart failure' covers a lot of options. In extreme old age, the body simply shuts down. Do you have suspicions, or what is the problem?
Dementia is considered by the medical community to be a fatal disease. It will result in death but the cause that appears on a death certificate will vary.
So to answer your question, there could be a number of ways a person with Dementia dies, diabetes, heart problems, cancer, the list goes on and on. Dementia could cause a person to not handle their declining health correctly and so could be considered a contributing factor in their death. But not the ultimate cause.