I'm also starting to lean towards this option. It is possible that the main writer Larian thought that taking away any opportunity to get a good ending for the most cheerful and pleasant character in the game is a good idea and that this is a “good tragedy” and the very “hope that kills”. In my opinion, this is simply selfishness and disrespect for the people who constantly kept Karlach close to them and were ready to do everything to ensure that her story ended well
