That is a good question. What is winning?
For Russia, a win is for Ukraine to change its direction or completely under Russian subjugation, otherwise what is the point losing that many men and resource and literally bankrupt the country just to get some land from Donbas (most of which they had already control since 2014 to begin with) Even if Ukraine is landlocked (Which is almost impossible now), it still process a lot of Military Power and if the Ukraine before that is a threat before, then what would you call the Ukraine that left behind with a lot of US and Western weapon?
On the other hand, you can say capturing Donbas would mean all those oil and gas goes to Russia, but then you will need to be able to sell it, EU isn't going to buy any more if they don't stop buying them altogether. And Russia can sell them cheap to India or China or Africa to earn some bucks, but with sanction and their economy down the drain, even if you can earn money by selling Oil and Gas, you can't exchange it anyway. Which mean this is going to be a moot point for Russia to just capture Donbas.
With the resource they had spend and lost, and the economy done for, Russia goal should be looking at at least a complete occupation of Ukraine, any less for them is in no way a win, not with all the price that they paid, or going to pay.