Lonewolf if you do not nip it in the bud and make sure that everyone understands that the only response to a nuke will be another nuke, then it opens China up to nuking Taiwan and Pakistan and India.
You have to have rules that everyone knows and understands that if you let that genie out of the bottle there will be a proportional and equal response, yes I maybe a relic of the cold war BUT the “rules” that have stood the world in good stead and have prevented the world from destruction then still are viable today.
Article 5 I think would possibly be invoked dependant on where a nuke was detonated, Kyiv for example would effect Poland
Meanwhile Russia is attempting to fill in the channel at the dam to restore access to Kherson.