That’s far from a foregone conclusion. NATO without the US is roughly the same size military as Russia, but Russia is currently massively outproducing NATO without the US and has more soldiers.
And then you have the possibility that when article 5 happens that the NATO allies pussyfoot around again and worry more about their own defense than the NATO alliance defense. In such a case, Putin can go pick off country by country and use them for cannon fodder against the next.