All Google needs to do is launch a superior LLM API on Google Cloud and essentially hedge their bets that any replacement for Google Search will be built on their API anyway. Or just spinoff a shell company so Google doesn't get bad PR for any bad results returned by their ChatGPT equivalent. Microsoft has avoided any real flak for the stuff that OpenAI releases
The other question is how does something like ChatGPT monetize to pay for the massive costs to serve queries? Google engineers have already tested this and say that LLM queries are orders of magnitude more expensive to serve than current results and I don't seen any paid service replacing a free search engine