Russia will never pull out of Ukraine. It is an existential struggle for them. They really believe that if they do not prevail in Ukraine, the US will station Aegis onshore systems in Eastern Ukraine (like they did in Poland and Romania) which will allow them to decapitate Russian C&C in Moscow with nuclear tipped hypersonic missiles with only a three (3) minute flight time to Moscow.

And I cannot say as I blame them. If the US had a sure fire way to do a pre-emptive strike that would destroy the regime in Moscow AND prevent them from launching any sort of counterstrike, don't you think they would do it?