At the moment everything is hanging in the air. The events of the next two days will really decide what happens in the next phase of the crisis. There aren't many grounds for optimism but here's some wild (or vapid) speculation. The main hope now is that the Crimean escapade damages the Russian economy so badly that it leads to Putin's downfall. I can come up with two scenarios where this might happen (they are not necessarily mutually exclusive):
1. The West imposes tough sanctions and squeezes the oligarchs until the pips squeak. As far as I remember, Putin's deal with the oligarchs was that if they stayed out of politics he'd stay out of their business dealings. Khodorkovsky violated this pact and was punished. However, Putin's politics are now likely to do significant harm to the oligarchs' business interests so they might consider the deal is off. They could react by removing him just as Nikita Khrushchev lost his power in 1964 as a result of his ill-advised adventurism (Cuban Missile Crisis, Virgin Lands Scheme). Yet, as we have seen, Russian energy and Russian sleaze has penetrated the economies of the EU so deeply that countries such as the UK and Germany may be very reluctant to squeeze the pips hard enough. I also have no idea whether, in practical terms, the oligarchs have the capability to get rid of Putin.
2. The Russian economy suffers and ordinary people's living standards go down. This inspires Orange/Maidan-style protests. Today, the opposition mobilised 30,000 anti-war protestors in a Moscow rally. But how much support does this movement have in wider Russia? At the moment, nationalistic fervour seems the order of the day among most Russians and Putin has tightened his grip on the media. If the economy tanks, though, he may face his worst nightmare: a popular revolt.
If Putin retains his grip on power, there will be a new Cold War. No Western country can ever trust him again after Crimea. The most pessimistic scenario is - it goes without saying - fratricidal bloodshed in Ukraine followed by a Russian invasion. We aren't there yet but so far the pessimists have outscored the optimists in their predictions.