The end will come with the collapse of the pitin regime predicated by collapse of Russian economy similar to the 90s.
China is the wild card as to how long this takes. My guess is China wants to bleed Russia for every man and gold bar it can, and then using pitin’s playbook take back the parts of eastern Russian federation Xi wants
Is the current Russian criteria for success in the invasion, not withdrawing no matter how many Russian soldiers killed and how much materials lost? No shortage of those in the West willing to oblige them.