If as you said that the Russian economy depend so much on the sales of gas and oil, then I think banning the sales of gas to EU countries will do Russians more harm than good. China will definitely take advantage of this situation since they are now the major buyers.
However, it won't be easy on the European countries as they now have to seek other alternatives to Russian gas, this will affect their economy as well. But as it's been said, necessity is the mother of innovation. They have been surviving without Russian gas and oil.