Energy is just not a very significant factor in Putin's calculus regarding the Ukraine.  (And neither is international finance, which you did not mention, thought the finance types at Bloomberg and FT still do.)

It is true that there might be some short term considerations and high prices in Europe for gas, but, because of high demand globally, Russia will easily find other places to dump its oil and gas reasonably quickly while Europe scrambles for other sources as well,and Russia does not need to export to get by, so it can easily weather any delays in finding markets. Energy is at worst a moderate inconvenience when viewed at the geopolitical level, largely because of Russia's relative self-sufficiency in all things that have to do with Putin's capacity to govern the country.

What matters in the Ukraine to everyone concerned is raw political power and not much else. For Russia there is also an added concern of national security given the Ukraine's proximity, but it is really power -- Putin's ability to do his job at getting Russians to agree on things enough to engage in collective actions  -- that matters more than anything else.  And since this crisis started, Putin's capacity to govern in Russia has increased dramatically.  This is working out for him, so there is little reason for him to stop.

For this reason, I think the only thing that can really guarantee the prevention of Russian tanks moving into the Ukraine is an invitation by the current Ukrainian government for a temporary, lightly armed (incapable of protracted offensive action against Russia) contingent NATO peacekeeping forces -- 20,000-30,000 people -- to be deployed in Eastern Ukraine to secure military bases or other strategic assets.  Russia is aggressive with its military where the US isn't likely to be forced to shoot, so a movement of US and other NATO troops, essentially as human targets daring the Russians to kill them, as Putin has been using Russia forces lately, would almost assuredly prevent Russian incursions in the Ukraine. While other paths are possible, I really don't think any of them provide the kind of guarantee that forcing Russians to kill NATO soldiers in order to invade eastern Ukraine would provide.  

And this is exactly what Putin himself would do if he were head of NATO instead.