Remove file from gallery may delete file

When you use the contextual link to remove the file from the gallery, the file is deleted (if it's not used elsewhere) by the file core module.
The file module compares the field value with the original one and delete it.

  // Compare the original field values with the ones that are being saved.
  $original_fids = array();
  if (!empty($original->{$field['field_name']}[$langcode])) {
    foreach ($original->{$field['field_name']}[$langcode] as $original_item) {
      $original_fids[] = $original_item['fid'];
      if (isset($original_item['fid']) && !in_array($original_item['fid'], $current_fids)) {
        // Decrement the file usage count by 1 and delete the file if possible.
        file_field_delete_file($original_item, $field, $entity_type, $id);
      }
    }
  }

We may change the confirm message that explains this file will be available to specify it won't if it's not used elsewhere in the website or people won't understand.

Example :

function media_gallery_remove_item_form($form, &$form_state, $node, $file) {
  // Set the breadcrumb.
  $node_url_arguments = entity_uri('node', $node);
  drupal_set_breadcrumb(array(
    l(t('Home'), NULL),
    l($node->title, $node_url_arguments['path'], $node_url_arguments['options']),
  ));

  $form['nid'] = array(
    '#type' => 'value',
    '#value' => $node->nid,
  );
  $form['fid'] = array(
    '#type' => 'value',
    '#value' => $file->fid,
  );
  return confirm_form($form,
    t('Are you sure you want to remove %file from the gallery %gallery?', array('%file' => $file->filename, '%gallery' => $node->title)),
    "media-gallery/detail/{$node->nid}/{$file->fid}",
    t('The file will still be available in the media library to use elsewhere on this site. Note: File no longer in use will be deleted.'),
    t('Remove file')
  );
}

Note: i'm using Media 2.x