Actually, the person to make this decision would have to be a family court judge (where the original order was filed) - considering your step-son's age, though, the chances that the judge will consider/grant his wishes are good.....depending, of course, on his exact reasoning for his wishes. Your husband, if as I assume from your post he is the custodial parent, will need to file a petition with the courts for a modification of the visitation order - requesting that visitation as previously ordered be suspended and that all future contact/visitation be at the boy's discretion (this leaves it open for him to change his mind by not completely locking out the possibility of contact between him and his bio-mom). As the boy is 16 the judge will likely request an opportunity to discuss the matter with him and get first hand the reasoning behind his wishes and then would proceed from there. From reading your post I would interpret it that the bio-mom left the area and there has been little contact?? If so chances are good that the judge will not force your step-son to try and mend that now and will not force the visitation on him. The reason I suggest this over him simply not going is it will avoid the chance she would drag your husband back to court for contempt for not allowing the visitation.
Good luck and God Bless
