Russia only have 2 options to win this war and both are bad
1) Full mobilisation and total war
2) Use tactical nuclear weapons or chemical weapons against western Ukraine and crush Ukranian morale using WMD.
There are no third option to victory. Longer the war drags on, weaker the Russian position becomes.
A third option is to go on defensive mode, rearm and return with more troops and tech. The Russians are fighting incredible numbers with far few troops.