If the USA goes out of the hockey business, there won't be a league that unites as much hockey talent as NHL does now. However, since the best players come from Canada, Russia, Finland, Sweden, Czech Republic, Slovakia, the impact on the game itself won't be as big as you think. The good games and the good teams would be more spread and not concentrated in one league. I don't think ice hockey would lose as much as you think if there's no more NHL.
The number one hockey country will still be Canada, followed by the European countries, probably lead by Russia because of the KHL.