Best case scenario is a revolution in Russia leading to a new democratic free country that immediately withdraws from Ukraine, starts selling gas and what not for needed cash and goodwill, sends war criminals to The Hague, etc.

Of course that's highly unrealistic. There is very little chance of a peaceful settlement between today's Russia and today's Ukraine (what Ukraine wants - its territorial integrity and probably reparations and war crimes investigations, is simply incompatible with the very nature of Putin's regime and situation), thus there's very little chance for Russian gas to flow as it did before any time soon. Hopefully by the time it's again possible it would have been replaced by alternatives.

Russia is already going broke. They could be forced to resume gas sales by financial need.