Don’t overlook the possibility of a divided Ukraine. The eastern half going to Russia, and the west staying independent.
Well it certainly worked for the best in your former neck of the woods, Slovakia. A "Velvet Divorce" probably is the best possible outcome.
That won’’t happen without a fight. Especially over Crimea, Kiev or the coal region.
I don’t think there will be any shots fired between nations and Putin will probably only engage rebels. Under the philosophy of “Ukraine can’t police itself from hooligans so we will”