Do you really think that if the USA networks walked away the cash cow Olympics could not replace that money?
American coporations require international markets and would look at the new economies expanding in Brazil, India, China etc
You think Visa, Coca-Cola, McDonalds will walk away from the Olympics if they are not held in the US. America is a saturated market, the rest of the world especially Asia, Africa, Latin America is virgin territory.
Could a reason the IOC are apparently greedy is not because they are needy, but because those existing deals are no longer as good as the ones they can get on the open market?