What does his contract of employment say? Does he have to work a period of notice? How important is he in the business and how easy is he to replace? If he has breached those he may be subject to penalties.
It sounds as if he is being pressured by your mother to take this stand. He is taking the path of least resistance and whilst he says he loves you unconditionally the fact that he is resigning shows very clearly that there are conditions on his affection.
A typical knee jerk response and it carries the threat that although he will do nothing for now, things may change in future. I would seek legal advice but witnesses are a self righteous bunch and love to gossip. Some may be able to justify working for an apostate but once they start putting pressure on them they will crumble. Start looking at how exposed you would be if every witness you employ resigns. Hope for the best and plan for the worst.