i dont think that we mourn because someone/thing is gone, i think we mourn because the/it meant (in a good or bad way) something to us and now that they/it is gone, the time is gone as well. and the story is almost over if not for the memories. memories are traces. and once the holder of these memories is gone, the traces will get more and more vague till they completely fade away. and then there will be no traces left on the face of earth and no one will remember our story. maybe we mourn because parting away feels like it never existed even though end is the best evidence of existence.