It seems like this could be incredibly fraught with danger once LLMs are involved (the story isn't exactly clear whether they are). If there are no surviving native speakers of a language (or very few) doing something like training an LLM to generate text in that language would run the risk of e.g. transferring English grammar to the vocabulary, and causing a hybrid language to become the dominant form of that language, because the LLM is used widely for study and the native-speaking elders are not.

Is that so bad? If the only way to ensure a language's preservation and continued use is to mangle and evolve it? I think that's kind of a neat concept, to be honest. To live is to change.