The integrity of Ukraine was compromised from the beginning. Russian naval station at Sevastopol, lots of Russians in the eastern part of the country and in the Crimea. Dependency on Russian gas. Never was a stable setup.
On the other hand, it is my impression Russia is despised by the non-Russians in Ukraine, more so the more westerly one goes. Putin might be strong enough to swallow that population, and clearly Russia does not shrink from incorporating hostile alien populations (as in Chechnya) per se.
But one has to consider the risks and the rewards for Russia. Clearly the Crimea is worth a lot to Russia strategically. That being the case, a good part of Eastern Ukraine is as well, being the broad land access. But western Ukraine? It doesn’t have the value to Russia of Crimea or of Chechen oil reserves, and would be a troubled place.
My guesses are no better than anyone else’s, but it would be my guess that Putin does not attempt to annex all of Ukraine, and perhaps not to formally annex Crimea or Eastern Ukraine either. After all, if he and his partisans control those two, that’s what really counts, and somewhere down the road there can be a vote in those places favoring “return” to Russia if Russia even wants to bother. There’s no great love lost between the Russia-favoring Russians in Ukraine and the western Ukrainians. (“Those Poles” one of them derisively called them to me)
And until such time as Russia formally annexes the Crimea and eastern Ukraine (if it ever formally does) our options in bolstering Ukrainian Ukraine are limited.
What we can do, however, and should do, is give a lot of support to Poland, economically and militarily. Pagan EU or no pagan EU, Poland is the front line showcase of what it is to be aligned with the West.
With Turkey going Islamist and the Middle East being rapidly delivered into Iran’s hands, there aren’t many places left where the West can do that.
Inasmuch as the Black Sea is going to be a Russian lake, wherein our only formal “ally” is unreliable Turkey, some thought ought to be given to Romania and Bulgaria as well.
Unfortunately, supporting the “front line” states competes with Obama’s goal of converting the U.S. into a pervasive welfare state in which all resources are devoted to internal dependency. If elected, Hillary Clinton will be no different. So, if the U.S wants to rejoin the world, reduced though its prospects now are, 2016 is all important.