What is life expectancy of late stage dementia patient?

Dementia: Usually rule of thirds. 3 years mild, 3 years moderate and 3 years severe.

Varies: Most people are diagnosed already in the moderate stages. From diagnosis most live about 12 years. You mention blood pressure so there may also be some vascular dementia mixed in. If health is otherwise ok, this individual could have a fair amount of time. Usually, when people stop walking & feeding them selves, they are near the end. Hope this helps. No matter what, make every day count!