I wouldn't confuse the value of the rubble to USD to the state of the Russian economy. As for inflation outside of a jump in 2015 due to sanctions hitting then it has been following trends that existed before the crisis.I am not even going to talk about the course of rouble. Memey example - pension in 2013 in USD was bigger than it is now, while it has doubled in size since then. That is how much the rouble "is worth".
How long do you think those reserves would hold up in case of shit?
Russia did take a hit in 2014/2015 but they adapted pretty quickly to the changing situation.