Let's keep oil price down for 1 / 2 years ... let's see how Russian so powerfull economic will collapse again.... as no money to fed up people but for War machine = endless credits :-)
Nothing will happen to Russia even if the oil price remains at sub-50 levels for the next 10 years. Because, Russia has other natural resources which can be exported (such as Coal, Uranium, Diamonds, Nickel, Timber, Potash, Steel, Chromium, Aluminium, Platinum, Palladium, Gold, Copper, Manganese.etc). Also, Russian defense sales are on the upswing, bringing in tens of billions of USD every year.
On the other hand, the American allies (especially Saudi Arabia and Kuwait) will be left bankrupt, if the oil price remains at <$50 for two more years. Already Saudi Arabia has started borrowing money. The fun will really start very soon.