I very much doubt that Google threatening to pull out of the country would cause any action in Congress. The government has no incentive to act, and all the power to spin the story if there is some sort of public outcry - something to the effect of "Google is unpatriotic and doesn't care about your safety." Most people will buy it.
If anything, Microsoft would just step in to fill the vacuum with Bing, and business would continue as usual for everyone but Google.
That's why I'm sayin' they can't just leave, and they can't just threaten. It has to be real civil disobedience. They have to be willing to say:
No, we're not going to do that. You'll have to shut us down, which will take years, and cost the economy millions of jobs and trillions of dollars.
Oh, and I hope it goes without saying that we won't be complying with any court orders related to this matter. If you're serious about doing this, there will be pictures of men pointing guns at innocent American technicians, right next to the headline "The Feds are Coming for Your Email," and underneath that, Senator, will be your name.
Then they'd say something like: "This is America, motherfucker. Land of the free. You can't get away with this shit."
A big multi-billion $ business deciding to dictate its own behavior or end is not the same as dictating law, even if the law reacts by changing in order to preserve the business.
The current system, where corporations often actually, literally dictate many laws is a lot less open and straightforward.
Big multi-billion $ businesses can only exist in a society where a big government can enable them using bailouts, quid pro quo campaigning and cost-prohibitive compliance for frivolous regulation.
From a societal POV, big anything is bad. I wish more open-minded people could recognize that fact.
That's not true at all; many (probably most) huge companies have never received bailouts. Compliance is also a tricky issue - you don't want to let the market compete on nuclear power plant design without some sort of supervision, even if the current system doesn't work very well. Lobbyists are a different story, but Google, for example, or Amazon, got to where they are without leaning on governmental support or anti-competitive laws.
If anything, Microsoft would just step in to fill the vacuum with Bing, and business would continue as usual for everyone but Google.