root/devel/mod/file/lib/groups_delete.php

<?php

// groups:delete
// When an access group is deleted, revert all files and folders restricted to that group to private

if (isset($parameter) && logged_on) {
            
    // Grab group ID
    $group_id = (int) $parameter;
    // Create 'private' access string for current user
    $access = "user" . $_SESSION['userid'];
    
    // Update files and file_folders tables, setting access to $access 
    // where the owner is the current user and access = 'group$group_id'
    set_field('files','access',$access,'access','group'.$group_id,'owner',$USER->ident);
    set_field('file_folders','access',$access,'access','group'.$group_id,'owner',$USER->ident);
}

?>