Don't forget that Canada also tends to be held to a higher standard here, like if they don't have a 20 man roster of NHL all-stars they're not going to be favorites. Just looking at Sweden for example, the best competition in 2014, iced players like Markus Kruger, Carl Hagelin, and Gustav Nyquist.
It's competitive because there's only so much ice time to go around with 18+ skaters, if they're all first line/pairing talents used to getting top minutes then a lot of the advantage is going to waste, and a team like Russia with a few elite talents surrounded by decent-good complementary players can compete with Canada.
Going by that model, McDavid could be the core player for team Canada for the next 20 years (assuming we get back to meaningful best on best competition). Then you also have a handful of top players still in there mid-late 20's like Stamkos, Tavares, Seguin, Benn, that could be in the picture another 10 years. If you need to dig a little deeper then maybe guys like Taylor Hall will finally get a chance.
All in all that gives a lot of time to and more drafts to fill in the gaps of expiring guys like Thornton/Getzlaf/Perry. 2014 (and 2018 if it were allowed) may be a peak no one else will reach for some time, but Canada should still retain the best roster for the foreseeable future.