Yeah and what would that do. Sure a lot of people would die but it won't help Russia win the war. If they shoot their load and they destroyed say two cities, then everyone else will know that's it. Launching the missiles would be literally the last thing that they ever do. Mutually assured destruction not required.
The best way to survive is to constantly threaten but never actually act. Eventually someone will do something about putting oil just die of old age. There isn't really a way there's ends with him being victorious.