They've been planning for this eventuality since the beginning. Remember that "Kiev in 3 days" was made up by an American general from the start of this armed conflict. The Western media will simply say that Russia wanted to take over all of Ukraine and overrun Europe but the brave sacrifice of your tax dollars (and hundreds of thousands of Ukrainians.... Whatever) stopped the Russian horde with on the sacrifice of a small amount of Ukrainian territory.
It's essentially the Finnish Winter War myth writ large.