Yeah are you sure you broke off the tip. All the cartilage should come out. There will be a good size hole, and fragile bones left. When I boil I don't leave the skull in for long periods of time. About 45mins. at a simmer. Remove what I can, and put it back in for 5-10 mins. I keep doing this until I'm satisfied. Never lost a skull yet. It also works best if remove all can before hand. The lower jaw, and brains should all be cleaned off.
If you did break the fragile bone off, I'd use some super glue, and piece it back together.