The people who are in oppose of bitcoins would surely die without food if this is the situation in the coming years where you can buy your stuff by paying bitcoins. And if it becomes mandatory even they have to buy anything using bitcoins.Even if they don't like it.
No they won't lol. When a country in EU had it's own currency and changed to €, people just came into their banks and exchanges and changed their currency for €, everything that wasn't changed for a new currency was worth nothing. The same thing can be done with BTC.
A hybrid of bitcoin and cash is still the ideal.
It would take a country with a pretty weak national currency to use BTC as official currency. Just is a lot of variation in value, which is hard as far as a government based money.
Bitcoin will need to stabilize on a price before it really could be looked at for a countries currency.