This is certainly a concern. However, I believe that if the NSA or local law enforcement have a way to mine your search history internal to Google, they will not be stopped in this endeavor just because you told Google not to save your search history. They can just gather the data in real time and maintain their own history for you.
The solution to this is not to turn off Google's search history, but to use a search engine (like DDG) who purportedly have security and anonymity built in.
The solution to this is not to turn off Google's search history, but to use a search engine (like DDG) who purportedly have security and anonymity built in.