How long do people with moyamoya disease normally live?

Depends. Adults with moya moya disease can live normal life spans depending on how severe the presentation is, which is usually a stroke. As long as there aren't severe or frequent strokes, there can be a reasonable life expectancy.
Depends. Morbidity and mortality rates are different in adults and children. The key is to establish the diagnosis as soon as possible as surgical treatment is proven to reduce risk of hemorrhage and neurologic decline.