Unfortunately, users will always be able to delete their own content, as well as those of other users when posted to a social group. In addition, place owners and admin users may also able to delete content for other users as well. This cannot be disabled out of box, so it may require customization if this is an important feature you'd like to see. Otherwise, I would encourage voting on De-couple delete permissions from place owner permissions or perhaps submitting an new feature request idea in the Ideas for Jive space to capture this need for our Products Team.
Let me know if you had any other questions with this.