Exactly, when Russia was being invaded, they lost a ton of people to defend their land. Doesn't mean they died willingly (people were drafted against their will, in every war in history that happens), but the pressure to surrender didn't mount up on the government. In a defensive war, people are more willing to die and to let their fellow citizens die. There are always people clamoring for an agreement or a surrender to avoid loss of life, but those voices are few compared to the ones who want to defend their land (or want others to go do it).

In a war of aggression however, every death come with a "why the fuck are we attacking them anyway? why did my son/brother/cousin have to die?". USA lost in vietnam that way. More kills, more money, won basically every engagement and still lost the war. If the population is against a war of aggression, it will end.

Very few wars end in complete domination of the enemy. Most end in an agreement of some sort or a retreat. I believe that, if Ukraine keeps getting money to stay in the fight, they will outlast Russia in political willingness to fight and will recover their land.