I know absolutely nothing about silkies. But, I would be giving him vitamins, yogurt and booing whatever you can to boost him system with good "things". I too have heard their skulls aren't closed completely and can suffer severe trauma to the head with what might be a slight injury. Unless someone more experienced in silkies pops in, I think you may be on a "wait and see" with this one.
I do want to say, chickens are fun, but it can be very sad and stressful when things happen that are out of our control. We do everything we know to be "right" and still bad things happen. I don' t think we should give up. Like the saying goes, "if at first you don't succeed, try try again".
Good luck. I hope your roo recovers.