Not really, they shut down the exchanges and its over for bitcoin.
That's like saying if they were able to shut down PirateBay then it would be "over" for Torrent files.
Reality: it wouldn't be.
I still don't believe that the government views Bitcoin in any way a threat to the current economic system.
1. If you purchase Bitcoin you need to use FIAT to get it.
...
Under the assumption (which I'm not saying remotely possible, or a given) that BTC became a widely used currency, fiat could be theoretically removed from the equation.
At some point, though yes, they would likely just collect tax from BTC transactions.
Bitcoin stands to shake up the current economic system quite a bit before then, though...
I think at first it's going to shake up with money services industry and that's who I would be worried about. Companies like Western Union (revenues of $5.7 Billion in 2012), PayPal (revenues of $5.9 billion, transfers of $145 Billion), SWIFT (revenues of $600 Million in 2011) and almost any bank who deals with wire transfers have a lot more to lose when Bitcoin is widely adopted. These will be the companies who will undoubtedly lobby governments to ban / restrict Bitcoins because it will put a huge dent in their revenues or if Bitcoin is adopted on a wide scale make them obsolete. Not complying with laws only gives them more ammunition.
I think it's naive to think that somehow Bitcoin lies outside of any laws or regulations. It is a revolutionary idea but an idea created in the context of our current political, social and economic systems. I believe it has the power to shape the future of those systems but we need intelligent and well thought out approaches to how to increase Bitcoin adoption not rhetoric about evil government or powers that be etc..
I totally agree with you on the approach being important, and who stands to lose the most. It's going to be a bumpy few years.