Siebe,
I think The Buddha compared the Parinibbana of an Arahant to the extinguishing of a flame, where it ceases to exist, and it would also be meaningless for us to say where it is going.
Please be very honest here: Do you fear becoming just like the fate of the extinguished flame once you attain Nibbana?
Is that why you are desperately albeit subtly trying to justify to yourself that there is an unchanging element that continues to exist after the attainment of Nibbana? That there is something lasting and stable to be found in a living being? That you can somehow exist as a silent and uninvolved observer (after attaining Nibbana) to witness or experience whatever goes on in the sansaric world, much like an observer watching a movie which depicts life, yet is basically not involved in whatever goes on in the plot of the movie?
You do not like the fact that there will be no more silent, uninvolved observer after the attainment of Nibbana?
Maybe there are others who think that we will just meld into Nibbana, yet continue to exist unconditionally. For me, I think that existence will cease once we attain Nibbana. Whichever the case is, it will not matter much once we attain Nibbana, for there would be no dukkha for it to even matter.
Do not be afraid of attaining Nibbana, even if it means giving up that which you desperately cherish — your deep-seated craving for existence. For you do not realize, just like me and most of the rest of us, that the enjoyments and pleasures of this world are just sugar and honey coated on the sharp, hurting edges of a dagger, which would surely hurt us sooner or later once we try to savour too much of it.
Although at the moment I cannot and do not realize Nibbana, yet I cannot explain why I have such deep faith, reverence and love for The Buddha. I do not even think I am a Sotapanna Anugami yet. Yet when I think about the tenets of other religions, I find myself unable to have faith in them. I would have it no other way, except to believe in Buddhism. That is why I am trying to persuade you to believe in Buddhism.
Try letting go of your craving for existence and control, and see what happens from there. The Buddha is immeasurably wise; He must have realized that Nibbana in whatever form it is, would be infinitely better than struggling along in sansara, no matter how pleasurable its traps and addictions are.
Perhaps you do not agree with my intuition and beliefs about why you are asking these questions. That is fine too, as long as I hope it triggered some deeper contemplation on your part, to aid you along in your spiritual journey.
Nibbana is not to be feared; please embrace it!