I don't think they necessarily do. Ruble is gonna crumble and pressure is gonna mount on them internally and externally. This is not a war that can go on for months. I'm not an expert by any means but I think it's one of those situations were you either win quickly or have to back down.
Agreed. If they did not have limited time, economic pressure, internal division, domestic unrest, disheartened soldiers... there's no question Russia would win. But they do have all those things working against them.
I fear though that the authoritarian state doesn't have the capacity to rationally analyze the prognosis and cut their sunk costs (both economic and political).