Aby_Z said:
Sorry, but the beginning of the end happened a long time ago, buddy. If you haven't noticed, natural selection has been all but abandoned. How can we put forth the best possible specimens of society to continue a string of reproduction that will lead to a superior race of beings much more fitted to survive in the world in which we ourselves destroyed without Natural Selection?
Here's your mistake. Natural selection isn't "The smartest" or "The biggest" it's "The most suited to their environmental condition." Darwinism doesn't save the world, it just keeps a species in it. Humans have adapted a society to keep themselves in the world. That's natural selection. Working together improves survival and breeding opportunity.
We've also done some phenominally stupid things which will test the survival capacity of living organisms on the planet. Those that can't adapt to warming and climate change will die out. Whether it's morally right or not, that's what's going to happen.
As to the topic, to my knowledge rockets are fuelled with various liquid propellants [http://en.wikipedia.org/wiki/Liquid_rocket_propellants] not all of which require fossil fuels. When using liquid hydrogen and oxygen, you only need water after all. As there is a finite amount of water on the planet us 'running out' of that isn't going to happen. However, the question is more whether we'll have the technology to utilise it and get enough of the population away, in the even of cataclysm, that they can start the species off again.
That relies more on the availability of habitable planets than anything. The ability to travel to them is also restricted by both fuel and technological advances. It's possible that we'll find something which will propel spacecraft to distant planets. As yet, no such luck.