Without the brain, you literally cannot live. The brain makes every thing happening within one's body possible. Even the work that the heart does is the brain's "fault". Take note that there are cases when the heart stops pumping blood for the body, which results more often than not to death. However, because of technology, ARTIFICIAL HEART may now replace malfunctioning heart. To make it super short, we may replace the heart but NOTHING MAY REPLACE THE BRAIN (for now, at least).