It might be that the Soul Society is not really "the final stop". It could be that the SS is place where the souls that are not so bad, but not so good go. If you die in the SS you go back to the world of the living to try again. We do know there are other realms out there other than the SS. So maybe there is a heaven out there and we just have not seen it. (As a note, did anyone ever realize that we have not seen a single famous person in the SS? No Einstein or Bacon or Sun Tzu ).