Living while Dead

What if someone was in like a  horrible accident and slipped into a coma for an extremely long time. What if while the persons body was unconscious in real life the brain kept going as if nothing had happened. As if  the brain created its own world with thoughts and feelings and everything a normal person experienced but set it up in the coma. Then the person woke up and had this complete shock of change and a shock of having to revert to the real world after being in this fantasy for such a long time. But what if also they never woke up and the family and friends of the person in the coma gave up and pulled the plug, would the person in the coma just die like in real life or would his brain have enough time left to create some way for the person to die in the fake world? Would the fake world become reality? What if you or someone you knew fell into a coma. Would you know?  Would your best friend remember you as you were or would his brain have made up changes for you?