Europe may need Russian gas, but Russia also needs Europe's money for the gas. And they don't have a plan B for raising extra cash. And even if in the short term they have to buy it, long term Russia is shooting itself in the foot.
Crimea faces a very difficult and uncertain future. It is a beautiful place with huge potential as an international holiday destination. But now it will become one of the world's outcasts, like Abkhazia, South Ossetia, Transnistria, Nagorno-Karabakh. Many, maybe most Ukrainains will leave, as perhaps will the hard-working Muslim Tatars, just when it looked as though they were going to be able to return to their native land. It's easily overlooked by the flag-waving grannies in Sevastopol that the peninsula is not really "Russian" at all. The predominance of ethnic Russians is largely down to Stalin's purge after the war.
In addition Crimea receives millions of euros in subsidies from Ukraine, which also supplies its water and gas.
Oddly, in the midst of all this, Dinamo Kyiv were still playing Tavria FC (Simferopol) in a Ukrainian leage game on the eve of the referendum (!)
As to whether Putin will move into Eastern or Southern Ukraine I can only say that if he does that he will unleash mayhem. And I don't think even he is mad or arrogant enough to think he could control the consequence. Places like Donetsk, Odessa etc etc are not like Crimea. There are few actual Russians there and people's opposition to Kyiv and Maidan is based more on economic fears than any desire to join Russia. There are a lot of provocations going on there just now, quite possibly much of it stoked from outside (Ukrainian Border Service has turned back hundreds of Russians trying to enter the eastern regions)
Thousands of volunteers have joined the newly formed National Guard, while local military units (Gorlovki) exist all over the country, Donetsk included, and have issued dire warnings about any Russian incursion.
In a news conference today Putin said he wouldn't "spilt Ukraine" as he "doesn't need to" Aside from the sheer arrogance of this, I would not trust the veracity either. If he announced that today was Tuesday I'd be checking my calendar ...