I have a hard time imagining what the best-case is among the likely scenarios for Ukraine, moving forward. Stepdown of their president, and then business as usual? A full military coup (like Egypt)?
It's likely now that Ukraine will end up getting split into two countires. To Russia Ukraine is a safety buffer between it and the EU, it's a matter of national security. Russia simply won't let Ukraine go, not without imposing severe economic sanctions, so Ukraine will suffer the split from Russia far more than it suffers now. On the other end, EU won't likely accept Ukraine with such sanctions attached. They already have Germany paying for Greece, Spain and Italy. Getting another mouth to feed will be hard to impossible to justify, regardless of how noble the motives are.
It's a stalemate. The only way forward for Ukraine is to let Russia have its safety buffer. If they want to join EU, they will have to split.
Well, things are at a stalemate now. Yanukovych cannot step down. He will literally be murdered if he does. His only protection is being the president. On the other hand while he remains in power the people will be protesting.
I think a likely course will be a "least of all evils" scenario. Yanukovych will make concessions to the opposition leaders who will then try to mollify the crowds. The EU treaty will be put back on the table and things will be dragged out for the long haul.
