Armies have momentum. Germany almost lost in 1941 when Barbarossa failed. Hitler managed to keep his armies from disintegrating, but it was a near thing. Japan's armies went far further then they had any right too in the same period, because of the perception of invincibility, higher morale, and everyone underestimating them for racial reasons. It's very clear that the Russians badly screwed up their logistics chain…
The Russian government knew there would be sanctions no matter what happened. They had already decided to accept those even in the event of victory. They aren't in a no-win scenario either. Kyiv cannot hold out forever. The Russians have an overwhelming numeric advantage and they can simply wait out the defenders, using that time to fix their supply lines. It's tempting to exaggerate a Russian setback into a total co…
As to simply waiting out, a clock may be ticking for Russians as well as for the Ukrainians. Probably not the same clock but still...