The starting idea is that there can be no definition of existence other than "something a consciousness can detect (directly or indirectly)". So if there is no consciousness, there is no existence.
But I think there could be a difference between death of all conscious beings, and consciousness itself disappearing. Consciousness could also be something that evolution found a way to tap into.
>Take the thought experiment of the boltzmann brain, it still requires the assembly of probabilistic entropy to occur, it is not nothing.
Yea, take that. I think the number of possible worlds where a simple life form spontaneously assembled and evolved to a human following the laws of that world, are enormously larger than a world where a full human brain spontaneously assembled all by itself. It is just statistics that we find ourselves in a world of the former kind and not a brain alone in an empty universe..