In my opinion, the use of a nuclear weapon is an admission of failure, military failure, international diplomatic failure and political failure. I'm not sure that Putin would see it like that, I believe that his focus now is on his survival and by extension the survival of the Russian Federation, any threat to that could trigger a nuclear escalation. That really only leaves the option of a military defeat outside his borders and/or his political defeat inside his borders. The latter would probably end the war in Ukraine, but only if his successor(s) have a suitable spin for their population. At the moment there doesn't seem to be any visible progress in this direction but that doesn't mean that it's not happening. I hope that Russia's 'non aligned' friends are taking and giving appropriate advice and counsel.