Even if a cornered Putin uses nuclear weapons, wouldn't the West be unable to do much more?

‌Russia is considering a full mobilization order,
and there are even strong reports regarding a potential invasion of the Baltic states
to block European support and allow for a full mobilization order.
Putin is in a very difficult situation,
but if he decides that Europe and the US can't do anything even if he fires nuclear weapons,
and actually goes through with it,
it seems unlikely that the West would be able to intervene militarily directly.
As for sanctions, there isn't much more they can do beyond what is currently being implemented, and Putin likely wouldn't even bat an eye.