When people get new bitcoins that aren't spendable in certain locations, it will be interesting to say the least. Then the government will force everyone to "accept all bitcoins".
There will be some groundwork done. Powerful people will be coopted. Developers, mining pool operators, exchange operators, merchants, whales etc. Propaganda will be used to convince ordinary users of the need for change. Then there will be a fork and whichever chain gets the majority's support will become defacto bitcoin.
Those who persist with the old chain will have their wealth instantly wiped out.Governments have a history of taking over private property. The Romans used to do it to every noble family that crossed the emperor. They even stole from soldiers who were away fighting for the empire!
When someone creates a bitcoin fork or spin-off, a user has two sets of coins: his original bitcoins and a new set of alt coins that he gets for free. Users don't really need to pick sides, as their wealth is valid on both chains.
Bitcoins will trade directly against fork-coin on the open market, so right away everyone will have a good idea of the value of a fork-coin. If a powerful group wants to legitimize fork-coin, they would probably sell bitcoins and buy fork-coins in an effort to shift perceived value to the new coin. But what about Satoshi? He would own ~1,000,000 fork-coins too (unless you also want to redistribute wealth on your fork); he could wait until you've spent all your bitcoins buying fork-coins and then dump his fork-coins for bitcoins, destroying the legitimacy of your fork and acquiring more bitcoins in the process.
Satoshi has more economic power than anyone to prevent a fork or spin-off from becoming legitimized.