You forgot couple important aspects: he also ruined the Russian economy (the conservative estimate is -12% GDP drop this year). Russian military industry also lost access to the Western high tech (unfortunately, a lot of it has been used in their modern equipment, such as missiles, aircraft, etc). It will take at least a decade for them rebuild the armed forces after the war with Ukraine.

There is indeed a risk of Kremlin using the tactical nuclear weapons. The United States needs to have a very robust strategy for such possibility. However, such use cannot be left without a response. Most likely it would be a military response. No response would set a catastrophic precedent, as it would invite the use of nuclear weapons in pretty much any conflict which involves a nuclear power. Just think about South China Sea, Kashmir conflict, etc. It would also lead to an era of nuclear proliferation, as weaker states would see no other option than to obtain nukes.

I think even the nutcases in Kremlin (or at least the Russian Armed Forces) understand that there would be an unprecedented response.