What is quickly ending the war going to do for Russia, except for risking higher casualties and giving Europe the room to breathe, as the latter is already going into austerity mode due to their increased military spending?

Russia’s only win condition in this war is economic in nature.

Remember, this is an industrial war - Russia can keep doing this forever while the EU is constrained by its monetary system and fiscal rules. The eurozone will not survive this if they truly want to defeat Russia in military terms. Europe ultimately has to make a choice, and all options available are worse for them.