Pretty much, if they attack first and we take out military structures in defense then no one will be against that. Nuking or doing anything first is the complicated part.If north korea shoot attacks first then china will back off but if we attack first then they will defend them http://www.dailymail.co.uk/news/article-4780602/China-stop-America-attacks-North-Korea-first.html
Will won't nuke them, but small tactical missile strikes destroying known military complexes and missile launching silos, then we could see an allied invasion of multiple countries into north korea to completely destroy the government and capture or kill kim jong un. I don't know what exact path they will take, trying not to kill civilians obviously takes priority.
The last thing china wants to do is start a war with the world, they will still uphold un sanctions against nk
https://www.thetimes.co.uk/article/china-enforces-un-sanctions-against-north-korea-gv8zk9z8q