Ukraine probably splits up. Russia will grab the eastern part and the western part will have a pro-Euopean government. Expect to see staged demonstrations in eastern cities over the next few weeks. A bunch of people waving Russian flags in the main square and asking Putin to send troops to protect them from the western criminals.

Probably a bit of military fisticuffs between Russian and Ukrainian forces but it shouldn't escalate too much. The west definitely won't get involved militarily. Some fairly ineffective sanctions which will be quietly dropped in return for Russian support over other issues a few years down the line when everybodys' forgotten about the Ukraine.