I don't get the injury concerns. Injuries can happen at any time. It can happen in his first game in the NHL. And heck, if injuries are a concern, why not just tank the last few games in his junior career? After all, he knew he was going to be, at minimum, 3rd pick overall. So why risk the injury playing the last few games of junior?
I agree with the others on here........you do what is best for your career. In this case, it is about actually getting some ice time. If the NHL starts on Jan. 1, then stay with the Rangers. If it is delayed until Feb, then get some playing time by participating in the best junior tournament in the world. And hey, buy some insurance.