I feel your entire post underestimates America.
The country would go batshit, for Russian blood. Sept 11th resulted in the US fighting over 20 years of war. Dec 7th resulted in the US ending facist regimes on the other side of the planet.
History shows that type of attack on a US target is unlikely to result in a positive outcome for the attacker.
The world is a small place now. If we ignore our neighbor being murdered, nobody will be left to care when we are murdered. If we ignore what is happening in Ukraine, it will happen elsewhere. Places we have defense treaties with. Better to fight the orcs now on our terms, then later on their terms.
How reasonable is it, is it possible to revoke Russia's seat on the UN Security Counsil?
A quick search on Google turns this up:
Can Russia be removed from UNSC?
Can Russia be removed from the UN Security Council? There is no mechanism to remove a permanent member of the Security Council written into the UN charter.
The only way to remove Russia from the Security Council would be to remove it from the UN entirely. This is technically possible, but has never been done before. Apr 29, 2022
That is followed by this gotcha:
The General Assembly may expel a member from the United Nations. But
a Security Council vote to expel a member of the United Nations is required before the General Assembly can vote on it. That preliminary council vote requires the unanimous consent of its permanent members. Apr 15, 2022
The UN is NOT intelligently constituted. Looks like we're back to sanctions and warfare.