What part of Ukraine? Not the part they currently "occupy", or as they claim have annexed and made a part of Russia. And which was in rebellion against the Ukrainian government for the past 7 years, and in fact were following exactly the "lesson of history" that those who go on fighting may rise again.
For the Donbas the "going down fighting" phase was 2014-2022, and the period since then is the "rising again and recovering their freedom" from the hated Zelensky / Kiev regime and their Nazi paramilitaries.
As you point out borders in this region and not immutable, they are quite fluid. You mention Poland's occupation during World War II, but what is probably a better model for looking at Ukraine's fate is the dissolution of the geographical nation of Poland in the late 18th century. There was no Poland on maps of Europe from 1795 until the end of World War 1 and the signing of the Treaty of Versailles in 1919. The victorious allies decided to break up the empires that had waged war against them, and devolve them back into smaller countries. Poland was recreated in the land that the Russian Empire, the Austrian empire and Prussia had annexed 125 years previously.
Map of Polish-Lithuanian Commonwealth before the Partitions, 1773.
Here's the same geographic area after the three partitions of the late 18th century. The entire area of Poland is now divided among other States:
Area of former Polish-Lithuanian Commonwealth after 3rd Partition: 1795
Partitition is the tranditional mechanism of ending conflict in this area. Look at the former Yugoslavia, for a more recent example. There were nasty civil wars there, but eventually everyone sorted themselves out into smaller more homogeneous nation-states and the world moved on.
This is a possible outcome for Ukraine at this point. Clearly it was not stable and successful as it was previously configured.
This 2010 election map shows the pre-war divisions in the country pretty clearly:
Russia is not the only country that is unhappy with the treatment of their linguistic and ethnic minorities in Ukraine, so perhaps future partitioning of Ukraine will attach Polish, Hungarian and Romanian enclaves to their respective nations, essentially something similar to what was done with the former Yugoslavia. Only easier, because Hunary, Poland and Romania already exist and are decent countires for their citizens.
Map showing the approximate dates when various parts of the entity we today call "Ukraine" were added to the country. As you can see, a lot of the territory that Ukraine claims is of relatively recent vintage.
Looking at the Polish example, after 140 years of being part of Hungary, Russia and Germany (Prussia) those areas were taken away and returned to the reconstituted nation of Poland. The resulting map was changed again, after WW2 when Russia kept a chunk of Eastern Poland and Poland was granted a chunk of former Germany.
Map of Ukraine's Historic Territory
The idea that these fairly recent borders are somehow sacred and can't be changed is stupid.
Partition, moving borders, and even population migration has long been a feature of resolving Central European conflicts, and it is likely to be the best way to end the carnage and destruction in this one too.