What would happen is that your son would grow quickly, but end up very short as his growth plates would close prematurely.  He would also go through puberty very soon, so therefore his voice could break he would need to shave, have body odour, acne etc.  I am not sure he would die as such but once he starts the medication he will need to stay on it as the adrenals may stop producing cortisol and he would become very ill.  Treatment does need to be started as soon as possible so your son will reach a reasonable height.  Good luck.