No, it will not delete photos and stories. When you upload a GEDCOM, we try to match photos back to names, but if a name has changed or there is ambiguity, the photo become unattached to a name. However, it does not get deleted. We have had instances where a user uploaded a "wrong" gedcom causing many photos to become unattached. This cannot be "undone". It you upload a correct GEDCOM after the photos have become unattached we cannot re-attach them automatically. You will need to do that yourself.
