Even shutting off the internet won't stop it. It's possible to send currencies with SMS if necessary.
And I really find it unlikely that the entire internet and SMS networks could be shut down in most of the world, anyway. Maybe in some heavily controlled places...
To me it's more likely that they may try gaining so much hashing power so as to render a network like Bitcoin under their control, essentially. But then one could turn to many of a number of other currencies, if necessary. They're better off just buying in and manipulating it like whales do (that's assuming they're not already doing so).
I agree that is the most likely scenario.