Demilitarization can only occur by conquest, or long war occupation
The retreat from Kiev signals that conquest was not possible
So an occupation by long war will carry out Demilitarization
NATO will not enter Ukraine because it would cause a defacto balkanization
So it will be this way for many years like Syria
The situation will evolve yearly
Kremlin will not kill kievan leadership, and will not topple the regime, nor attempt to build any kind of real state there
Kiev will be left alone
But attrition will plague Kiev and Russia for many years