Lots of doomsday scenarios can happen.
Consider also that, as dominant companies see their revenue slip, they start cutting corners and get complacent with security.
Yahoo is the prime example, I think. It was one of the giants of the early web. Then they started losing relevance, hit rock bottom, started cutting corners and as a result 500+ million users had their account details leaked by hackers.
Another doomsday scenario is Google being bought by or merged with a competitor that doesn't give a shit about your privacy or your data.
So this entity gobbles up Google's data, sets fire to their privacy agreement (which they will pretend they no longer have to honour because they aren't Google) then pimps you to the highest bidder.
Bottom line is, we're screwed.