We lived once thru this in 1939. NO one will join in to defend Poland. Germany might even make another deal with Russia to "save EU".
Also most Russian don't seem to be even close to being as enthusiastic as the majority of Nazi Germans were when their tanks rolled into Paris. Russians seem to be mostly apathetic, they don't really support the war but also are not willing to actually stand up and do anything about it. That might change if there is not quick victory/large amounts of civilians start being killed/sanctions actually start working.
Once the coffins start to come back to mother Russia domestic support for occupation will plummet even further locally in Russia.
Even in USSR, with censorship and active repression USSR was still bringing back afghan war coffins in the dead of the night.
The situations in 1939 and 2022 are only similar insofar as we are talking about the same country. Everything else is different.
Czechoslovakia would probably be a much better example (however NATO did not exactly agree to recognize the annexation of Crimea and the Donbas just to appease Putin).