Germanic tribes, and this continues over to Ukraine culturally (because Rus), had the battle cry “better dead than slave”. A village would fight down to the last woman, elderly, and child. Because even if the aggressor overcame them they’d be left with nothing but their own losses. Thus, they wouldn’t even try.
If Russia is allowed to get away with this, Taiwan will be next. A gazillion of small-scale empires in unstable regions all around the world will say “well, seeing that noone cares our time to get away with it”.
Millions if not billions of people more will be dead.