It seems to me that if Bitcoin passes a certain threshold of user adoption, it will be like the WWW. There have been alternatives in the early days, but they are all gone.
But then, Bitcoin may be scalable to one Million TX/s, but what if you have e-butlers, doing many fully automated micro payments for you? Bitcoin may have to scale 2 orders of magnitude higher. If Bitcoin is not up to that, it obviously can't be the only game in town.
Similar if Bitcoin is outlawed. It will not go away - it may even grow faster. But if outlawed, it will stay underground.
[EDIT]: The only "nothing" scenario I see is if the Net is locked down to unprecedented levels. Like every computer comes shipped with spyware, every payment must be processed through the government and violations of law carry really harsh punishments - in short, a HiTech North Korea.