I think you seriously underestimate Russia. They have a helluva lot of manpower, natural resources and money. They are also able to import western sanctioned materials via China and Central Asian countries.
Russian society is being organized to resemble a war economy. There are new laws that make drafting more difficult to avoid and with more severe punishments. Also they have just raised the age for conscription. They are playing the long game and preparing for future eg. mobilizing the whole society under one delirious cause. Late 20s, early 30s it is totally possible that Russia has a better military capacity than it currently has. Sure, the life of average Russian will suck way more than it does now, but there’s not really an option if you want to keep your job in a tank factory and avoid going to prison. You have no choice but to participate.
Putin has made his mind and the struggle in Ukraine only makes him more determined that He is fighting an existential battle with the west, especially since he believes that democracies and western liberal lifestyle are on a path of inevitable decline.
Sure, if he is stupid enough He might start a conflict with NATO, believing that the alliance will break when under pressure. He might think that He is prepared and the west is weak. And while there’s 95% change that he is mistaken, it doesn’t matter if he himself believes the crap the yesmen around him and He himself are feeding him. That’s the real risk and to me, a defeat in Ukraine makes this scenario less likely to happen.