Every once in a while, my brain will wander down the rathole of, say, being killed. Dying. Either just me or most of human civilization. Nuclear war, comet striking the earth, storms, floods, victim of a terrorist plot. You name it, it could all happen. These are all considered "doomsday scenarios." "The world is going to end," they say. Well the world might end as we know it, but the reality is short of something causing Mother Earth to explode, the planet will continue to exist. We might not.
We do not exist separate from the environment in which we live. Until we figure out how to get off this rock and colonize other worlds en masse, we're stuck on the third rock from the sun. Anything that happens to Mother Earth happens to us all. A friend of mine once likened the planet to an organism of sorts. We are a small part of Mother Earth—cells in the larger organism. Mother Earth's "organism" could determine that we are a "virus" that needs to be taken out. There are plenty of examples throughout history of Mother Nature having her way with humanity. I have no doubt it can be even worse.
Now I might sound like a fruitcake, or at least a rabid environmentalist. Believe me, I'm not. I don't attempt to live a carbon-neutral lifestyle or force my views on the world. There are plenty of things I do that I recognize aren't the "best" for the environment. That being said, I am in favor of things like recycling, using less energy overall (either through increased efficiency and/or less usage), and occasionally sharing my views with the world.
The important thing to remember is that the world will continue on—with or without us.