Why?
Poroshenko can’t stop the Russian army.
And Afghan-style insurgency works only if the Russians are stupid enough to move into Western Ukraine.
Putin won’t take the bait.
Poland cannot sit idly by if for nothing else, they don’t want a bunch of Ukrainians fleeing into Poland.
Poles and Ukrainians are good neighbors, but you don’t want them both to be under the same roof.
Eastern Ukraine is full of ethnic Ukrainians, Russians are just a sizable minority almost everywhere and many of them are neutral about the conflict. Russian invasion of Eastern Ukraine will mean millions of ethnic Ukrainians living under occupation.
I read a report about two injured Ukrainian officers who exploded themselves with grenades, killing some Russkie soldiers, when they were about to be captured. I have a suspicion that Ukrainians are going to give it a good try, regardless of what some surrender-monkey Paultard and Russkie thinks they should do.