A CVA and its subsequent depression, would have no survival value what-so-ever. The CVA (depending on its site and severity) would probably render the individual immobile, or partially so, unable to communicate, and therefore, unable to hunt or forage for food and therefore, become prey for animals. Depression does not have a "survival" function, rather, just the opposite, as it effects are contrary to activation, cognitive processing, mental inefficiency, and lethargy etc. For depression is a brain state.