I do not believe in God, nor an afterlife, nor reincarnation. I believe we each get just the one life, starting more or less from scratch. I believe there are no supernatural entities who will clean up after our messes, nor that there are any other worlds available to us should we render this one uninhabitable to us.
Certainly I agree with Carl Sagan the odds are great that there are many many planets with life in some form throughout our galaxy, but that life may be alien to us, as may its ecosystems, and any worlds in our galaxy that are habitable to us are out of our reach for the foreseeable future, perhaps forever. I agree with Sagan the odds are good that some of that life is intelligent, and some of it older than we are, and therefore some fraction of it must be wiser than us. Unfortunately, the galaxy is huge, so the odds are poor that we will ever have the benefit of alien wisdom.
So, in summary: no additional lives, no additional worlds, no supernatural or alien wisdom available to draw on, no one to save us from ourselves. This is it.
In the film Contact by Sagan, Palmer Joss makes a statement I have heard from several religious people I respect, that they would not want to live in a world without God. I understand. We have treated the world and each other as though it and we are disposable, as though there are second chances, as though someone wise and wonderful were waiting in the wings to make things better. If we live our lives that way, we must go on believing it to insulate ourselves from the horrors of what we are doing. If there is no second chance, then the full impact of our blunders is unmitigated, and the bleak prospect of extinction shockingly looms over our children and much of life on Earth.
Whether we treat it so or not, life is precious. This one world that is the mother of life as we know it is precious. Each of us has but a single precious life; we shall not pass this way again. Wisdom and compassion are precious.
You are precious, Dear Reader.