Some observers have also said that the split was based on age as well as geography.
Younger Ukrainians (so the theory goes) who came of age after independence, tend not to identify with Russia.
What happens to them if Putin takes over?
If RF overruns the Ukrainian military and occupies the entire Ukraine, there will be, most likely, a terrorist activity that would make Chechnya look like a garden party. Putin cannot put the entire Ukraine in a GULAG, even though he will try.
Observe that it is not 1945-54 when Stalin exterminated the Bandera rebels. NATO will quickly toughen up because it is an existential threat to them; they will set up a full blockade. The Russian economy is not going to hold together in order to sustain a prolonged guerrilla war while under sanctions.
Even an annexation of Eastern Ukraine is not going to be easy, given the passions that have been stirred.