Bitcoins will be hard for them to stop without shutting down the entire internet. Should a government act against bitcoin, it would drive the price through the roof.
i doubt every governments will ever work together, so this scenario is very unlikely, you will always have at least one government that will not do anything against bitcoin, many have already embraced it, so why, suddenly, they should go against bitcoin without any reason? no-sense....
Government can't stop the adoption of BTC, sooner or later they're going to realize the benefits that it can bring.