Suppose Verisign one day went crazy and suspended Google.com or refused service, can they even do that? Or just simply refused to allow Google to renew the domain and then took it for themselves?
Most likely, they would find them in a highly expensive civil lawsuit they'd ultimately lose at the expense of billions of Dollars, so in short: I don't see that happening.
The real issues would rather be smaller organizations with no good legal standing, like e.g. bitcoin.org.