The idea is the Opencoin will not own Ripple, and that Ripple itself will be decentralized. The system won't be worth anything without gateways, but at the moment I don't see any clear reason why gateways couldn't operate legally. If they comply with the same laws as regular banks do, why not?
Some gateways might, giving the authority less of an excuse, however I suspect that many wouldn't comply. This probably would give them an excuse to try shutting down the entire network.
Of course we hope for the best scenario, and that the resistance of status quo is not too violent. However I think it's a given there will be plenty of bankrupcies of scummy gateways, and excuses to shut the whole thing down would be abundant.