Russia has 140 million people, the world's 11th economy, and, despite the impression one might have watching the news, only US/Europe (plus usual dependencies in Asia) have imposed sanctions on them. That is to say, there is still a lot of trade between Russia and the outside world (and the central bank does not seem to be printing money like mad).

Edit: It looks like the 50% drop only last a day. The rubble has since steadily somewhat recovered to 'only' about a 30% drop, which may also be due to Russian government intervention.