According to the UN, at least 192 groups have successfully done that.
No. They started a security force and claimed sovereignty over property and land of
other people.
+1
Where would violence come from? Austrian commandos storming the Federal Reserve? A nuclear exchange between Mt.Gox and Paypal?
I don't see it.
The simplest most basic scenario I can imagine is employees fired due to obsolescence of their work power.
Other case scenario might be that massive ammounts of people start saving in BTC and banks reserves go dry which would obvioously led to bank runs.
Not predicting any of this will happen, just thinking what may happen given proper conditions in a reality not that different of today.