Honestly, if Kiev does not surrender and accept Russia's demands, particularly regarding neutrality, Russia can do much more than just the creation of a buffer state. It can turn Ukraine into a landlocked country and wait for it to become the second Moldova, or even worse. It won't take much time for the Ukrainians to change their minds then. If you look at the map, the Russian forces are already advancing fast in the Southern front, probably planning to disconnect Ukraine from the Black Sea and the Sea of Azov.