Gretzky retired in 98-99. It did take 15 years, but NHL hockey implemented rules to make the game less brutal and it seems to be working. Players crashing into each other head first is not an inherent part of the game like it is with American football. Sure concussions occur, but it's got to be a fraction of what happens in football.

http://www.wsj.com/articles/professional-hockey-has-become-a...

"Much of the decline can be attributed to fewer players going to the box for the game’s more violent infractions. Charging, boarding, roughing and cross-checking are being called at the lowest rates since 2001-02, according to Stats. It seems that the NHL’s plan to crack down on violent penalties this season is working."