Well it wouldn’t be half of Ukraine, it would be about 20% by area and less than that by population.
Its worth noting the fighting for Ukraine to keep that 20% is done involuntarily. People are literally being forced to die, make their partners widows, traumatise their family, for this 20%.
It’s easy enough sacrificing hundreds of thousands of other people’s lives (I’m assuming you’re not typing this from the donbas) for this small rural farming end of Ukraine, but that doesn’t make it right.
I deliberately chose a high number, because I’m saying there’s no reason this would satiate Putin. He has no need for those 20% land. Why should he stop when he gets them?
If he would restart the war, why is he pushing for peace talks?
The war is both going worse than people expected it to go for him, and Russia is also making progress.
Stopping the war, then restarting it risks a restarting of the war being impossible due to Ukraine signing security treaties with NATO members, and Ukraine building it’s army up as a result of this war. Furthermore, given rolling the “invade Ukraine dice” went worse for Russia the first time than expected, why would they, or any similarly inclined nation, do it?