Once bitten, twice shy. I think the days of Russia being a supplier of oil and gas to EU are over. No EU country is going to get into the trap of depending on Russia's energy again. And that is no matter how the war goes or if they withdraw or if they are completely defeated. Doesn't matter.
Unless Russia completely withdraws, apologizes profusely, sends some of its leadership to stand trial in the Hague and negotiates a reparation plan, there will be no end to sanctions. I have researched this extensively, using Russian sources, and the conclusion is, with current sanctions they cannot even drop to the level of 1970s. They will start at somewhere in 1950s and work their way up. And good news - they basically cannot maintain or develop their military under sanctions. They stopped production of missiles and tanks. No machinery to produce new artillery pieces either. It is not even foreign electronics. It is the complete destruction, starting with the 90s and to today, of the domestic machining production. Every lathe, all metal fabrication equipment, everything is foreign sourced and there are no new machines or parts or even software upgrades. You have to start at the level of nuts, bolts and ball bearings - the production of all those is sub-par in Russia. Then build your way up.
I really have no idea what the leadership there was thinking. I think they broke the "don't get high on your own supply" rule. They actually believed their own propaganda that the West is weak and will just fold. They are finding out just how wrong they are now.