I will not rush to the conclusion that Europe is doing well without Russia's energy because, from what I have seen in the media, they are not doing very well. If they're really doing as well as you claim, their inflation hasn't been in double digits for the past 40 years, and things aren't getting any better either. Russia does not have an energy monopoly but is the most perfect supplier to Europe, if Europe had a better supply, they would be different now.
The biggest challenge Europe is facing is the competition. A large portion of Europe's economy depends on access to
cheap and reliable energy, when that is disrupted (even a little bit) the competition from other countries (China, India, and a dozen other countries) take over their markets very fast. Hence the deindustrialization of Europe.
I've said this many months ago when they were celebrating the fact that Russia was selling its oil/gas to non-European countries at a big discount. There was nothing to celebrate about because that was the first step of ruining EU economy.
This is why we see today that Europe's economy is at least $1 trillion smaller and continues shrinking while many other countries are expanding their economies.
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The same arguments could be made about defeating Russia in any other manner (LBMs and simple tanks, weak rockets, etc.) in which case I see your scenarios are still valid since a losing Russia could still decide to go nuts and use a tactical nuke since this is not a war Russia can afford to lose.
BTW this is exactly why those who aren't benefiting from this war always suggest a diplomatic solution to this conflict.