The way I see it, Ukraine has been unstable for at least a decade. This whole east vs west didn't come overnight, it's been going on for years and politicians have been unable to adequately adress the situation. In stead they blamed each other for everything that happened in the country.
When Tymochenko was in power, the west supported her and the east didn't, when Yanukovich won, the east supported him and the west didn't. What the eastern parts of Ukraine didn't do, was overthrow the government when Tymochenko was in power, something the people in the west did when Yanukovich was in power.
Crimea now had it's taste of Russia. They've got the ruble, they've got Russian as their language, they are Russian basically. If you put them back into Ukraine, you'll create so much instability in Ukraine that eventually the whole country will blow itself up. It's basically what's happening now between east and west, only then Crimea will start a third group. It'll be hard enough to create a sustainable peace with these two groups now, let alone when Crimea joins the revolts.