Yes, Russia has a finite window in which it can bring in its tanks and heavy artillery, which are its strengths, before the spring thaws mire them in the mud. It's not entirely clear what the endgame is here, though. They can not sustain an occupation, and they will suffer heavy casualties if they do a street-to-street urban war; they will face questions at home if heavy Russian casualties are incurred, which is entirely possible given the US and UK have armed the Ukrainians up the wazoo with antitank missiles; they can not sustain a 'fortress Russia' with $630 Billion in USD reserves indefinitely; and they certainly can not stop the long term turn towards NATO and away from Russian energy exports, which will get a jolt in the arm after this disastrous war.

> It's not entirely clear what the endgame is here

Fuck up Ukraine and go home. Belarus has already been turned into a puppet state, and if they manage to turn Ukraine into a similar puppet or at least a failed state, there will remain no prosperous alternative in Russian-speaking world to Putin's Russia.

Russians have massive inferiority complex since at least the 1960s when Soviet Union began to significantly fall behind the West and this is their way of dealing with it.