In my view, Sampan, that scenario would appear to be a defeat for both sides, really.
The EU, if acknowledging that break-up, and after repeatedly asserting that Russia is an aggressor against peace in Europe, would concede that military intervention (i.e. war) is again an acceptable way of changing borders in Europe. Something the eastern european states especially would certainly fiercely oppose.
To calm those nations, a much heavier NATO presence on their territory might be necessary. Something that goes in a circle of not defusing at all the tensions between Russia and much of Europe.
On the other side, the ukrainian parts you see as going into the EU via their "parent states" would by the same token also become part of NATO right away, as all those "parent-states" are already NATO members. An eventual "core-Ukraine" might find it easier to join eventually. That all, NATO borders moving closer to Russia, seems to be the prime thing Putin is strenuously trying to avoid with his current actions.
With all this on my mind, I currently do not see the reasoning behind your proposal / prediction.
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A pro-NAF reporter doing a news coverage from the Debalsevo about how there's no ceasfire has (inadvertantly and again) filmed russian tanks there.