"Russia cannot sustain the war effort at this cost and this pace for the entirety of Ukraine. "
That is something I heard ... since the beginning of the war, yet I see no signs of it. Russias economy is in full war mode, producing way more tanks and shells than the west. Ukraine has serious ammunition and manpower problems and the front can collapse. Also Ukraine prepared for a succesful offensive, and neglected the defense.
"It’s a really small place with minor strategic value"
And that small place was one of the best fortified places and succesfully defended since 2014. The fallback positions are not nearly as good prepared. And the chances are low, that they can even fallback with no more roads under their control. It is really not looking good at the moment.