You are making an assumption that Russia is unaware of this. Russian military's declared objective is demilitarization of Ukrane, meaning, degrading the capabilities of its conventional force, and to impose a regime change. Russia if it is going to stay in Ukraine, they are going to withdraw to the east of Dnipro and to the south and they will easily control that territory.
1)Voting pattern of 2010 presidential election ( it's this government that wa overthrown by west Ukranian nationalists)
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2) Ukranian parliament election 2012
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3) Ukranian presidential election 2014(after coup d'etat) Pro Russians were banned/ boycotted in this election
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Such political and geographical polarisation makes Ukraine very vulnerable for foreign occupation. Their ability to put up a united opposition is limited.
Now take a look at the percentage of Russian speakers in Ukraine by region and you can see why this divide exist and why Russia is likely to pull back to east of Dnipro and to the southern costal regions after destroying Ukrainian Military.
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