Hell, maybe the afterlife IS alien (yes I realize by technical means this is already true). But Imagine if our existence and all of creation is actually from the work of the most intelligent and most evolved life form in the universe. In essence that is what god is, but I'm not proposing a SINGLE source of power but an actual race or group. While this would pose the question "well what created them/it?" that question already exists for god anyway.
Now there is a belief already called Raelism
http://en.wikipedia.org/wiki/Raëlismwhich is basically that belief that we are the biological creation of another species. I personally think Raelism is silly but still an interesting concepted belief.
I think it proposes an interesting idea which can still be reflected upon. What if "God(s)" and the highest beings of the afterlife are actually the extent to universal evolution? Not only beings which evolved to the point of creating life (something even we humans have at least conceived with the idea of cloning) but also beings which evolved to the point of discovering Lazarus or immortality, by means of biological death and becoming capable of weaving the two together. Of course we can't conceive of these ideas now but it makes sense if you factor in evolution which whether you believe it or not EXISTS.
Evolution is a natural part of time and life. I've been alive since the the mid 1980s and just looking at how the world has changed since then is pretty wild until you really think about how far we've come since 10,000 years ago. Now imagine where we are now and if our existence continues imagine evolution another 10,000 years from now. As a species and as a society we would be pretty incredibly formed and if you consider that all new discoveries are still being made today (think about the mass amount we don't even know about the universe OR even the ocean) it isn't inconceivable to imagine that even humans could one day discover how to create life from scratch and completely understand life after death.
Maybe our "god(s)" is simply the highest evolved life form before us. That isn't that ridiculous to me. It's no more ridiculous than a supreme being of infinite knowledge and power residing in another realm, and even if our biological creation was not from the hands of god that doesn't mean it doesn't exist.
I actually have more of a theory that "god" is only the creator and energy which makes up the essence of "life" itself and it was something else which created biology, our bodies, and nature of this planet.