It is difficult to know what will exactly happen, after all as far as I remember the only country that has declared bitcoin as a legal tender is El Salvador, a country as big as Russia and with such a large population will bring a new set of challenges to bitcoin that it has never faced before, so I doubt that it will help Russia that much to do a movement like that at this moment, however if the sanctions keep mounting then the Russian government may be forced to take a decision like this and hope for the best, even if they know the potential positive effects they could expect would be on the low side.