Not quite. Russia's reserves stand at about $409 billion, according to their own central bank. Monthly values | Databases | Bank of Russia
This down about $79 billion from the same time last year. The last reported numbers are end of Sept, and they have thrown perhaps another 5-10 billion at protecting the ruble in October. They have a leak. At 10 billion a month, they would be good for more like 3.5 years. That assumes that the lower price of oil somehow does not continue to hurt them even worse, which it definitely will.
What they need is a rebound in the price of oil. Short of that, they are in serious trouble.
And you assume that Russia will sit there and take no necessary actions.
4/5 years is plenty of time for Russia to cut public spending to take into account lower oil price and also take necessary measures to stimulate the non oil/gas sectors of their economy. Oil prices are only down 20% not completely collapsed.