He's a triplet, so his skull is naturally thinner than the average person. Plus it was never a break, but rather a depressed fracture. That sort of injury takes years to fully heal. And by years you're talking about him wearing it for the rest of his career as a precaution. I'm in a similar position with my knee. I simply cannot play in goal without my knee protector/brace, my body just refuses to dive because I have a subconscious fear of damaging it. It's there as much as a psychological protection more than anything.