When a goat hasn't been disbudded (and Emmett hasn't, judging by the pictures of him) their horns have a blood supply and nerve system. Depending on how far up the crack is, you could be risking it breaking off and exposing all that, it can actually be a fairly traumatic event. Your best bet is to try to stabilize the horn and support it best you can until it grows out. This is one time where you are blessed that you only have one goat - he probably doesn't butt all that much without another goat to butt back, and right now that's a saving grace. Try to get a good safe epoxy or something on the horn - failing that, even duct tape is better than nothing.