I honestly don't know if the bone will ever be covered - you'll find out as the wound heals. Euthanasia is certainly an option, but so is giving the wound a chance to heal if the roo doesn't seem to be suffering too greatly...and that's your decision to make.
It's also possible, even if you don't see external wounds, that he's suffered internal injuries. My personal philosophy is to try to help unless it's clear that's not in the animal's best interest. It would be very informative if another BYCer could share their experience with an injury of this nature.