[When trade using traditional means is restricted it is only natural for involved parties to seek alternatives.]
Changing currencies won’t change the basic reality - companies can sell to the US or they can sell to Cuba, but not both. While Russia would like Europe to be able to push back, the fact is that Europe is a collection of independent states, many of which are either US-leaning or understand that their ability to avoid becoming Russian oblasts rests on American military power. Now, there are any number of Russophile leaders in Europe, including Angela Merkel. But Central Europe, which is right next to the Russian hordes, will prevent the anti-American elements of the EU from organizing a united front against Washington.