The NHL will adapt to our ever-evolving technology and it will be a virtual sport with simulated players on the ice rather than a live one, thus solving the player safety (concussion specifically) conundrum. It will still look realistic enough to draw an audience but attendance overall will decline, but the sport itself will grow as technology will allow it to be global sport.
Junior players will continue to play in their current leagues and drafting will continue as is. Following their draft, they will run a series of tests similar to the combine where they will be measured up against the perfect hockey player (rated 100 in every skill) and will be given a score, and based on that they will have a virtual hockey player created based on their realistic skills. NHL players will also go through these testings prior to the start of every year, thus continuing to require extensive off-season training. The game will be far more focused on skill rather than the physical aspect, since virtual players hitting each other won't result in real-life injuries or any sort of damage, the physical aspect of the game will be diminished and not nearly as valuable as it once was.
Players and teams will have their virtual game at the arena, where they will be hooked to a machine that wires a connection between their brains and their bodies and they will enter the virtual ice and play the game. Technology will allow the players to play based on their reported strength, stamina, creativity, shooting, etc. so each player will still have a defined role, regardless of what line they're on.
I think the world is already headed in that direction as it is, we see it in games such as golf and baseball, and even in past live events such as coachella that drew thousands of fans for holographic performances.
