I agree with aojumper that armaggedon is taught by many religions, though I have never heard it to the extreme that the witnesses do.
That being said, though, as mentioned above, there is nothing we can do about it. We have no idea if it will even be in our lifetime. Thousands of years have gone by with nothing happening. It could be tomorrow, it could be another couple thousand years.
Either way, if we sit back and worry that it is going to happen any moment, we will be very miserable. We need to live productive active lives, and enjoy our time here. What happens later will happen, and we deal with it when it does.