Maybe he has nothing to lose from threatening. But he would have a lot to lose (namely Moscow, and any place where he's known to usually spend time) if he actually fired a nuke at some EU capital.
I'll bet that that would not be Paris or London. But to try to guess what someone who has nothing to lose will do is folly, Putin might very well be beyond caring even about such stuff: he wants his legacy cemented and there are two ways out of that that would satisfy him: the fact that he is remembered as a great Russian or that there isn't anybody left to remember what kind of an idiot he was.
For some idea of this mentality, if you haven't seen it yet I highly recommend the movie Der Untergang, which is as historically accurate as they could make it, and which gives a unique perspective on how things could get so bad that parents would poison their children to avoid them having to live in a world where they weren't the victors.
NATO article 5 is a meaningless piece of paper in and of itself if the will to retaliate isn't present and we will only find out about that at the moment someone wants it invoked. I would not necessarily bet on knowing how that ends. The response against what happened just now is underwhelming, and the various investments in fomenting nationalism/isolationism may well pay off. These are very dangerous times.
> I highly recommend the movie Der Untergang, which is as historically accurate as they could make it
And in case anyone didn't make the connection, is also the movie where the scene used in all those "Hitler hears about..." YouTube clips is taken from.
