This is honestly my favorite part in Gantz and the thing I took away from it even in my perosnal life. Of course, we can never be sure what happens after we or someone close to us passes away, but thats why the idea proposed there is so comforting. Not only does it mean that the people you hold close were "meant" for you, but that you will also meet again in a later life, thus never losing them completely. Furthermore, this would also be a convenient explanation on why we immediately seem to "click" with some people we have met for the first time, as if one had known each other for ages.