new search engines when google leaves?

The only substitute which is anywhere near as good as Google is Bing, it's an obvious answer but Google is one of the worlds most famous brands, so you would expect it's closest equivalent to be pretty obvious. No other English language search engines have comparable indexing and searching capabilities.

I don't think Google will leave though, it could be possible that someone could somehow come up with a vastly better search engine that everyone would start using instead of Google, but then that would also become famous, so you would know what it was.