Section 6B. In the event that either of the petitioning adopting parents to a petition for adoption, which has been filed with the probate court, should die prior to the entry of a decree of adoption, the probate court may enter a decree within three months following the date of death nunc pro tunc to the date of the filing of the adoption petition. Said decree shall have all of the effect of a decree of adoption as to both petitioners and the person adopted as provided for in section seven.