Your brain cells don't get replaced, and the only neurons that still enjoy the wonders of neurogenesis in human adults are in the hippocampus but that doesn't mean that those new neurons are there to replace old ones dying, so what the author says on page 9 is already wrong.
Anyway i wonder how the ship of theseus will come into play, the concept of authenticity and cloning is hardly ever done right in fiction let alone manga, plus it has so many cool stuff attached to it, like immortality, the problem of identity and self, and sure it all can be just linguistics, but it can also be a real problem depending on the philosophical stance, anyway this could be really interesting and hype, i wonder if the author can deliver on the things that come with the paradox.