If there is no communication whatsoever between Russia and the rest of the world (highly unlikely), then the network will fork. The main chain the rest of the world follows will lose the Russian hashrate, resulting in longer block times for a maximum of two weeks until the next difficulty retarget. After that, things would continue as normal. The Russian miners would either stop mining altogether or continue to mine on their own minority chain. Once internet communication is reestablished, then either the minority chain would simply be abandoned in favor of the main chain from the rest of the world, or the minority chain would continue as yet another fork of bitcoin.

What is far more likely is that there would still be a handful of nodes which could still communicate to both sides of the divide, and so the whole network would stay in sync. Users in Russia might see more frequent stale blocks and stale chains if it takes them significantly longer to remain synced with the rest of the network.