Yeah, that's less common. Most kids figure it out well before that age and I don't think any of us were traumatised. Kids break down crying all the time, but a few hours later they're fine. Anyway, it's your job as a parent to prepare your kids for life--heartbreak and disappointment are part and parcel!
I'm torn on the issue myself, not sure if I would tell my kids he was real. I remember when my cousin decided to tell her daughter he wasn't real when she was nine and she broke down crying. Kids naturally trust us and believe what we tell them, it seems cruel to make them believe in such a wonderful thing and then break their hearts a few years later. Then again maybe you don't have to tell them at all, at some point they usually figure it out themselves.