Google makes its money from advertising, but in order for it to place ads it needs to serve relevant results; serving "tailored" results because they generate more clicks is short-sighted (well, that's the argument anyway). If people become so distrustful of Google that they stop using it, and use a combination of DDG or Wolfram Alpha for example, then there will be no more ads for Google to serve.
We're admittedly very far from this, but the fact that high-profile people such as PG start to complain about it publicly (and not just old anonymous grumps like me) should make Google think.
or Google could serve ads by developing a suite of web apps, or a mobile operating system, or a even a social networking site.
Google could even serve ads on other people's websites when people visit those websites without going through their search service.