Any currency can be propped up for a period of time by its central bank and government but the end will be a stunning and drastic crash. If Russia is ever able to freely float its currency again, speculators will take care of that. We’ve seen it before, speculators knowing the true value of a currency versus a central government fighting to prop up or peg their currency inappropriately.
In the mean time rubles are like casino chips they are really only good in the casino. The only reason anyone would want them is if they are going to that casino.