That's why they're conquering not just the east but all of Kiev, Odessa (Ukraine's only remaining black sea port) and the chicken neck near Moldova. They can trade away these if necessary, for everything east of the Dnieper.and I think some of the land taken will be used as negotiating points to get ride of the stricter sanctions
because Russia cannot live with the sanctions for a very long time their economy is getting hammered and would want some of them to be lifted
the only other thing is the mutual trust and friendship over last 8 decades with Germany is lost and also they have lost trust with Scandinavia nations who all contributed to Ukraine with ATGM including Finland
the fall out will be massive but just shows how far Putin was willing to go to keep Ukraine
honestly Ukraine should have just let go too many are dying and the destruction is too much
no one knew how much Putin wanted Ukraine if they did they could just have it for heavens sake
It is unlikely for Kiev to remain capital of either west Ukraine or east Ukraine in this situation. They'll probably move the western capital to Lviv and the eastern capital to Kharkiv.
Now west Ukraine will have a dilemma: if they recognize Russian control of the east they can join NATO. Otherwise they can't because they have a "disputed territory".
But recognizing it means they lose east Ukraine forever since now there's a militarized natural barrier: the Dnieper River. Their only real choice is to accept Russian control of the east and join NATO/EU with something like ~12 million population with 2000 USD GDP per capita after losing their biggest industries and resources to Russia. They'll be a permanent drag on the EU.
If they don't join NATO and EU due to rejection then they'll become a failed state.
That's my prediction of the Russian end game: take as much of Ukraine as possible but at least east Ukraine, and make the western part a failed state.