If there isn't a plothole, I think Larian is trying to be too subtle here. While bits and pieces of story/lore does provide hints of a feasible explanation, I think a more direct scene early on to address this loophole will be for the best.
For better or for worst, pointing out plot holes has become a pretty prevalent in main-stream entertainment critique (not that it's necessarily wrong, but just that it's become a much bigger point of focus now more than ever due to a few catastrophically produced movies and tv shows). Whether our tadpoles are different from the others, the plot hole of "death = the solution" can be addressed by variety of feasible in-game discussions. I think we can even come up with ways in-lore to address the revivify and resurrection magic in general. For example:
Example Explanation 1: The tadpole is so parasitic that it has inserted itself into the blue print of your body, as if it was a part of it. Meaning, even resurrection magic will be tricked to restore the tadpole as if it was a part of you.
Example Explanation 2: The tadpole is bound to you not just on the prime materiel plane, but also the Shadow Plane (hence the Netherese magic Ethel freaks out about). You need to remove the tadpole from both planes in quick succession, otherwise as long as one of the links exists, the tadpole will regenerates itself into your mind (could be an interesting mission down the line)Regardless of the explanation, I think a few earlier scenes and observations needs to be made to make this follow better:
- The first time Tav or a Companion dies in combat, there should be a scene/dialogue exploring this plot hole. Maybe even let the player try various methods to destroy the parasite (though might be too gross). The key is to show that if the dead companion is revived, the Tadpole is revived with them.
- Depending on whether our tadpoles are the same as the other True Souls, some scenes need to be retconned. I.e. if they are the same, then the Tadpole should not leave Guts or Edowin's body (and these scenes can be used to trigger the above dialogue)
- Various NPCs (i.e. Halsin) can provide more exposition later on about the special nature of these tadpoles.
