It doesn't have multiple chains, it has one. Which means if there is a blockchain the whole world agrees to, and we all use it, then suddenly Russia goes out, just Russia goes out, the blockchain continues like nothing happened. If Russians are somehow trying to connect to it, they will fail, so they will have to create their own coin.
Consider it like BCH, bitcoin cash was created from Bitcoin blocks as well and became its own coin, Russians basically will have that. Bitcoin has only one, and it can't be separated like that. If you really want to find a better way, they could just use a VPN to access bitcoin even if the government blocks them.
That's not how it works. If Russians run the exact same protocol as the rest of the world, then there is one coin with two competing chains. If the Russian nodes every see the other chain from the rest of the world (which will have more work), then they will abandon the Russian chain and swap over to the other chain.
It is not the same scenario as bcash, which was deliberately forked from the bitcoin protocol and therefore incompatible with bitcoin.
How many North Koreans you have seen around this forum?
If you were a North Korean who had gained access to the rest of the internet, the last thing you are going to do is advertise that fact and draw attention to yourself.