It will not benefit Putin to "level" Ukraine. He would have much better results if he can succeed in QUICKLY toppling the pro west goverment, installing a friendly government and taking advantage of a productive Ukrainian economy. As said before if the military and civilians can give him enough problems and casulties and mire him down, it would be in his best interest to back off and stick to "claiming" the pro Russian areas of the country lest he risk undermining his "support"(forced as it may be) amongst his own nation.
