They don't have the luxury of time. With NATO becoming more and more aware this isn't a bluff you can be sure they will be shipping in more and more cheap anti-tank and anti-aircraft missiles to Ukrainian ground forces which are highly effective against russia attackers as they stand. If Russia starts firebombing cities I think they might win from demoralization but it could also get Russian citizens and politicians nervous and sick to watch Putin destroying their brethren in Ukraine. You have to remember Putin is a sociopath and while intelligent he doesn't have any real emotions to understand that total war against Ukraine could easily end support from his country and allies like China and neutrals like India.and Turkey