For many, the thought of ceasing to exist at some point is indeed frightening (for others, it's tossed off with a shrug of the shoulders). Are we nothing more than the inevitable structural results of a math-based universe full of law-abiding particles? Like I said before, the only way to know for sure is to die. I think it's a nagging question that will always be a part of the human condition. I do think that the worst response to the question is to act as if you know the answer, but one can operate under an assumption based on the evidence available--which, right now, is none.