Andy
It won't be the Ukraine that starves Europe of gas, it will be Gazprom effectively backed by Putin. Military action by Russia is simply out of the question, to do so would put Russia's fledgling market economy back 10-20 years with unthinkable implications for foreign investors and their colossal investments. IF, military intervention was seen as the only option, then I suspect the EU, if not the U.S.A. would underwrite Ukraine's natural gas bill for a few years. After all, considering the millions the EU has poured down the black holes of certain Palestinian's secret bank accounts for the past 20 years, whats a few hundred million more for a visible return? Whereas, in reality its a question of who is going to blink first - Russia, or, the EU? Both have much to lose, with perhaps the U.S. the least and only too happy to see the EU having to face a major issue and showing some backbone (for the first time).