Does the stomach muscles heal completely after hysterectomy ?

Depends on the route: If the hysterectomy is done through an 'open' abdominal procedure (either a 'bikini' cut or an up and down incision in the middle of the abdomen) the rectus abdominus muscles are separated in the midline, and may not heal together completely (something called a 'diastasis' or separation of those muscles can result). If it was a vaginal hysterectomy, or laparoscopic hysterectomy: yes they do heal.