Not much more than the lifespan of the brain+body. This is because of aging: risk of death follows the Gompertz distribution, which is worse than exponential.

Not much more than the lifespan of the brain+body. This is because of aging: risk of death follows the Gompertz distribution, which is worse than exponential. Or, another more intuitive way to put it: brain diseases are already a leading cause of death among the elderly. (Stroke, Alzheimer's, senility, some cancers, arguably accidents/falling, etc.) So even if you evade heart disease completely, it doesn't buy you all that many years before another thing gets you.