Completely agree with his decision to leave the game before it made matters even worse. Head injuries are no joke. I had a few concussions while playing high school sports and now just a few years removed from that I already have experienced some effects from them (e.g. more frequent headaches, migraines, stuff like that).
One thing that strikes me as odd though is why during the season the nature of what his injury was wasn't fully disclosed. I might be wrong, but I can only remember Urban vaguely saying that he was "dealing with something" and can't recall anything official from the team saying he had a concussion.