How long to people diagnosed with benson's disorder generally live and in what condition? about how many people are believed to have been diagnosed?

Not very much known: Benson's disorder (posterior cortical atrophy) is believed to be a visually impairing variant of alzheimer's and is very rare. See this landmark paper from 2004: http://www.Orpha.Net/data/patho/gb/uk-benson.Pdf a consult with a neuro-ophthalmologist may be helpful.

Few yrs, rare: Benson's syndrome (also posterior-back brain-cortical atrophy) is a rare neurodegenerative disorder start in vision cnter with inability to recognize familiar objects or people. It is a syndrome, because it can be part of another disease, such as alzheimers or jacob-creutzfeld). Mild to severe, 1 to >10 yrs, stable for yrs or progressive disability. First 2 yrs at specialized center is crucial.