I dont think it will work , Ukraine is a plain country and Guerilla warfare is not easy in plains and Russian intelligence might have penetrated in Ukranian military so carrying out such tactics is not easy.two things the Ukrainian army should do to win
1- start a guerrilla warfare on large scale ( not less than 250k people )
2- make this war to last for more than a week
Best is to talk negotiate , hopefully they save some lives and prepare for another day .
Moral of the story is don't rely on western powers as far as your country's security is concerned