I would cull it. It would be picked on, not to mention it would be highly suseptable to disease...and you dont want it infecting healthy chicks. Sorry.
Yea, I can't believe it, no idea if there is any chance of the skull growing over...if it did somewhat, it might have a chance at being an indoor chicken, maybe?
That doesn't happen often. Honestly, you need to cull it. With exposed brain like that, even in the house, there is chance for serious infection. I'm sorry, that's really awful.