I can’t believe you’d discuss this situation without considering the nuclear angle. Putin holds a significant wild card in terms of tactical nuclear weapons.

I’m sure Russia believes that they could be deployed inside of Ukraine in order to force an end to the Ukrainian resistance and the west would continue to remain on the sidelines to avert escalation to the end of the world.

A total defeat/humiliation of Russia without nukes flying seems like a remote possibility. Putin realizes that defeat signals the end of his regime and likely the Russian Federation as constructed today, just like the Russo-Japanese war led to the end of the Russian Empire and Afghanistan war led to the end of the USSR.

Right now there lacks Sun Tzu’s “golden bridge” across which Russia could retreat in dignity.