This type of dementia produces symptoms such as causing disruption of perception, thinking and behavior. The hallmark symptoms of this dementia are more psychotic in nature, such as hallucinations and delusions, and symptoms that are similar to those of Parkinson's disease, such as stiffness and rigidity, frozen stance, balance difficulties and tremors. However, as in many diseases, the symptoms can manifest themselves differently depending on the individual and similar to Alzheimer's disease, the rate of decline varies for each individual, though the average duration for LBD is approximately 5 to 7 years.
I'd echo both of the earlier responses. My mom (who had Alzheimer's, not Lewy body dementia) also had Chronic Obstructive Pulmonary Disease (COPD) for smoking for far too many years. The COPD actually claimed her life, not the Alzheimer's (although I believe the combination of the two diseases made her Alzheimer's progress more rapidly).
Hope this helps! Take care!
As with most types of dementia, much depends on how healthy the person is otherwise. The dementia will eventually kill the person, but most people live longer if there aren't other health factors involved. Only a doctor who has examined the person could give a educated opinion.