Wikipedia doesn't have to shut down, but they have to remove the libel.
The problem for LLMs is that they do not learn, and can't be prevented to produce that libel ever again. If Google finds a way to make that happen, no court would stop them from offering an LLM.
The court isn’t stopping them from offering an LLM, it’s saying that serving the output of its LLM is, in this sense, equivalent to serving the output of a human writer they hired. That is, it is Google’s speech and they are directly liable for it, unlike when they’re just serving search results that are somebody else’s speech.