bsilver is right. Eventually, our sun will begin to die, and when stars die, they first go supernova, expanding many times over. Earth will be completely destroyed at that point. However, it is very likely that humans (and, indeed all life) will have died out long before that. It is, of course, possible, that humans will have migrated to other planets by that time, but we are talking billions of years here, a time frame so huge as to be essentially inconceivable for us.