Russia can't sustain this war, nor can they occupy their gains long term even if they do take the Dombass.
The red line has been drawn, the west will not lift the sanctions as long as they remain in Ukrain.
They got a pass on the Crimea but this time it's different and the sanctions will eventually suffocate them.
Right now they have the oil and gas to bring in their blood money but for how long?
With the west now actively looking for other sources to stop the reliance of their oil and gas the much needed funds will be cut in half.
The russian population will suffer and there is only so much suffering they can take, there will be a breaking point.
It's all "for mother Russia" just now but the Russians have to a certain extent being been living a western life, with their designer goods, Iphones and PC's and now thats all gone.
Theres also the elite, oiligachs, again they can take it for now but again for how long? When will they use the power and influence (money) to turn this around.
There is a lot of kinks inthe Russian armour, it only takes one to break.