I think they are enough. Even if ratings are goin down, we are still talking about the olympics.
Now, I am too lazy to go and check the figures for the various area since it does not seem possible to get worldwide date, but if I remember correctly the Tv data were lower than Sochi in Europe, but the streaming shattered records. I also remember reading something about record viewers in Asia and Australia , but that I think is related mainly to the time zone. Bbc also had some record numbers.
Anyways, hockey is just one of the many events in the olympics, the nhl presence is not that likely to affect the figures significantly on a global scale.
Of course, other factores are, as you said, so it is very much possible that the ratins will continue to drop, I just do not think that the nhl can affect that.
Anyways it seems that now they have been forced to go to the right direction, both Milan and Stockholm presented very cheap and "sustainable" candidatures, that rely mostly on already existent structure scattered over quite a vast area.