His paternity can be disestablished during the divorce if that is what he chooses. It doesn’t appear that is what he would choose. Depending on all of the facts, it could be a court would not terminate his parental rights, even if the mother wants to, especially if bio dad doesn’t step in and act. Courts have been known to continue a legal parentage in such situations based on the best interests of the child. Much info is lacking here so what might happen is impossible to guess.