Earlier quoted context omitted.
It's also possible that the government may declare some bills invalid (what happened in India with larger bills). Also, government could inflate away your wealth by printing more currency. At end of the day governments control both the network via (ISPs & Networking equipment) and processors (Try producing an 8080 in your backyard.). You make mistake of assuming that countries won't put up a global firewall that make…
Governments are not a conscious entity that is separate from society. They are institutions run by a collection parties with numerous competing and aligning interests, and with extensive stakes in society at large. They're not going to do something as massively destructive to society at large as ban encryption and prohibit all microprocessors lacking a back door.
Bitcoin/Ether barely register in terms of the total economic activity (75 Billion $). With significant fraction unusable. They will either be tamed or destroyed.
In fact another way of looking at cryptocurrencies is as a revolt against the Visa/MasterCard duo-poly & regulations that has made digital transactions too difficult. The moment digital transactions become cheaper/more-efficient, the allure of crypto-currencies will disappear.