Cosmology is important to consider with the question of an afterlife. In a theistic cosmology, God created nature. In a nontheistic cosmology, nature simply exists on its own, having no beginning or end. Since this is an atheist forum, I will show where a nontheistic cosmology leads as far as an afterlife is concerned. For this post, I will not consider consciousness in a vacuum, but only with an associated physical system.
As you read this post, you presently have a perception of your existence. This perception is supported by your biological system. It could just as well be supported by another biological system. In a nontheistic cosmology, there is an infinite resource of space-time through the infinite quantum foam. With such an infinite resource, your present perception of your existence, defined to any finite precision, is certain to have infinite instances of existence through the space-time infinity of the quantum foam. I do not believe that reality is limited to nature, but if I were to limit myself to a nontheistic cosmology, I would see this as the most rational conclusion.
As you read this post, you presently have a perception of your existence. This perception is supported by your biological system. It could just as well be supported by another biological system. In a nontheistic cosmology, there is an infinite resource of space-time through the infinite quantum foam. With such an infinite resource, your present perception of your existence, defined to any finite precision, is certain to have infinite instances of existence through the space-time infinity of the quantum foam. I do not believe that reality is limited to nature, but if I were to limit myself to a nontheistic cosmology, I would see this as the most rational conclusion.