What would happen if people lose trust in Google, success-wise? If they stop believing that the good people at Goole will keep their servers running forever, let their spiders crawl to get the latest internet content and make sure that the search results are excellent?
When people lose trust in the success of a shareholder company, they try to sell their shares before they become worthless, which makes them worthless really quick. That could happen to Google one day, of course.
But there would be another dimension: Everyone would rush to get his data from Google before the servers are dead. Gigabytes of Gmail conversations, Google Analytics statistics, Google Calendar Entries, Google Reader collections. Imagine Google does have technical problems, and then we all, at once, try to get our data back. Then they have technical problems (Even if they don't have technical problems I think it would be hard to survive such a data rush).