

The level of consciousness in something like a brain parasite or a slug is probably so dim that it barely feels like anything to be one. So even if you were reincarnated as one, you likely wouldn’t have much of a subjective experience of it. The only way to really experience a new life after reincarnation would be to come back as something with a complex enough mind to actually have a vivid sense of existence. Not that it matters much - it’s not like you’d remember any of your past lives anyway.
If reincarnation were real and I had to bet money on how it works, I’d put it down to something like the many‑worlds interpretation of quantum physics - where being “reborn as yourself” just means living out one of your alternate timelines in a parallel universe.
In the book “The World Without Us” the author states that old steel bridges would be among the last human made structures left thousands of years after humas have dissapeared for the reason that they didn’t have strenght calculations back then which they solved by simply overbuilding everything.