What are the long-term complications of dementia?

Progressive. Dementia generally is a fatal progressive illness.
Dependent all ADLs. End stage dementia is characterized by needing assistance with all activities of daily living including eating, toiletting, etc. End of life in dementia is caused by an inability to swallow and immobility and the complications arising from these things - pneumonia, urinary tract infection, bed sores, dehydration and many other possible syndromes.
Death. Dementia is a progressive non curable disease (most cases) where brain function deteriorates including recent memory, orientation, capacity to take care of ourselves, capacity of rationalization, inability to be responsible, inability to make simple mental mathematics, insight about the disease, even speech and mobility change. There is degeneration and atrophy of the brain.