Eventually, Russia is going to run out of stuff. They are able to produce war materiel at about 1/10 the rate it’s getting spent on the battlefield. However, Russia has a fucking lot of stockpiled stuff.
What Russia is attempting now is to hold out until Trump gets into office and Ukraine’s support is slashed. Then they might win. But they are already cutting it close, using thirty-year-old rocket engines and tanks donated by movie studios and the like.