I hope to god that this does not blow up.
It will most likely end up with some Russian military action inside Ukraine, but I think that it will remain localized, even within Ukraine, and certainly won't spread beyond Ukraine. As much as I think Putin is a dangerous dog, he is a smart dog too and I think right now he has a pretty good grasp on just how far he can push against the political inertia of the US and Europe without getting into a real shooting war with either.
The end result, I think, is that by the end of this year the eastern parts of Ukraine will have been annexed to Russia the way that Crimea is now annexed to Russia.