The Government isn't some omnipotent god-like overlord of the people. The Government is limited to work with certain enumerated powers. Destroying Bitcoin is not one of the powers they possess...
Cryptography isn't new and it's already withstood the government's attempt to destroy it. The government attempted to regulate cryptography as "munitions" in 1993. They lost... The Judicial Branch of the US Government has already safeguarded cryptography. Combine Bitcoin with the Fifth Amendment against self-incrimination and Bitcoin is pretty much secured. You cannot be compelled to reveal your private key if you choose not to... DPR was facing a laundry list of charges; no doubt he was compensated in some way for that private key, he agreed to the deal; whatever it was...
"Two federal appeals courts have established the rule that cryptographic software source code is speech protected by the First Amendment (the Ninth Circuit Court of Appeals in the Bernstein case and the Sixth Circuit Court of Appeals in the Junger case)."
Bitcoin regulation is not possible; USD regulation pertaining to Bitcoin transactions is within the regulatory authority of the Government but it's thin ice because it's illegal to restrict USD transactions for political protest. Bitcoin by nature is a protest against the current financial system. Choosing to use Bitcoin is political protest as protected by the First Amendment; using a competing product is protest be it subtle or not...
The Government destroying Bitcoin is equally as likely as the Government declaring Martial Law and throwing political protesters in FEMA camps... It's just not a fight they're in a position to win and it's not within the scope of power that they possess.
They would need to change several previously existing laws, the Judicial branch would need to reverse its stance on the First Amendment, and then to make matters more complicated, any laws that restrict Bitcoin would also restrict other digital tokens of common use, the digital marketplace would essentially collapse and that's a huge financial sector in itself.
"In the abstract, spending money can be considered a form of speech in the same way that throwing a brick through a window can be considered a form of speech. The issue is a question of balance. Nobody believes in protecting the right of the brick thrower to “speak” by committing an act of violence over the right of the window owner to be secure from destructive acts." --
http://www.amendmentgazette.com/how-spending-money-became-a-form-of-speech/