They want to make Ukraine a federal state.From that perspective it means permanent war. No government installed by the Kremlin will be regarded as legitimate. It will be extremely costly to install such a regime in power. Propping up such a government will require a great expenditure of resources. What Russia can much more easily maintain is constant harassment of Ukraine at the border areas as long as a government in Kiev has a hostile posturing towards Russia.
It will looks like this :

Federal goverment with very limited power, independent subject, with federal level constitution that contain all security gurantees fo Russia, to change it they need say agreement from all subject of the federation, and probably many more requirement.
The individual regions could do they independent elections, and they could elect the representatives of the federal goverment.
Russian military units in sealed bases, probably federal level guarding of the borders.
The regions could fix the issue of the local resistance.
Long term it could be the model for the baltic + belorus.
A federal country composed of Belorus + Lithuania + Estonia + Latvia, with the Ukrainan federal model.