If we want to postulate the geo-politics of a Russia so crazy as to launch a nuclear attack (hoping for no response), we can also look at the effects of having a Russia so reviled that they become the focus of the entire world's fear and hatred.

Would having a single known enemy make for a more unified and ultimately productive world?

Check my answer to another post of yours. I doubt Russia will launch an unprovoked nuclear attack but I would not put it behind them to escalate conventional war to nuclear if it will start going badly.