Hi Siebe,
When a person enters Parinibbana, it is not the end of the being. But an end to a process. A process whereby this being is reborn over and over again has ceased forever. Thought, feeling, perception, and consciousness will cease without remainder. Kind of like extinction. The reason why it is so horrifying to most people is because we cling on to our life so dearly so much so that we are afraid of losing the ability to cognise things.
Due to the notion of a self, we developed passion. And because of passion, we think there is a self. I would think this is the Paticca Samuppada steps ‘sankhara paccaya vinnana’ and ‘vinnana paccaya sankhara’, respectively. A self is an artefact of our consciousness, just like the concept of time. An enlightened being who had passed into Parinibbana would be timeless. He would have attained infinite steady state of bliss where there is no concept of time. In Parinibbana, there is no arising of consciousness. And since there is no consciousness in Parinibbana, there is no concept of time.
A true buddhist should not view rebirth as a continuation of life. Instead, he or she should view rebirth as a perpetuation of death. We are born only to die. Whatever worldly things we wish to accomplish in this life, we had done that countless number of times deep in our past lives. One really needs to grasp the concept of infinity. I think it helps tremendously and I managed to debunk many myths and superstitions just by contemplating on infinity.
Which brings me to a question – Does the Universe serve any purpose? :)