the picture is not so clear but anyways the dimple inside if no clinical such as gas or stool or urine comes to vagina normally might not be a fistula . Commonly that I found the dimple like this might be the skin fold because the camera might not deep enough and vagina are not fully open so it cannot get to the deeper part or the fold inside the vagina that mimic a dimple like this but anyway, better go to gynaecologist or Srs surgeon to use a vaginal speculum and recheck again
from my experience, I think it might be better to sewing at least the posterior midline to reduce the dead space and more convenience for cleansing but it 's also have opportunities to heal by itself but you need to closely observed , need to keep it dry as much as possible with tampon and local wound care and antibiotic and check for sign of infection . and make sure that you can get through your vagina correct way when you dilate not going through the wound that will make it worse .
