/**
  * Automatically run when a block is deleted. This removes the special data from the block's specific database table. If a block needs to do more than this this method should be overridden.
  * @return $void
  */
 public function delete()
 {
     if ($this->bID > 0) {
         if ($this->btTable) {
             $ni = new BlockRecord($this->btTable);
             $ni->bID = $this->bID;
             $ni->Load('bID=' . $this->bID);
             $ni->delete();
         }
     }
 }
<?php

defined('C5_EXECUTE') or die(_("Access Denied."));
Loader::model('sortable_responsive_gallery', 'sortable_responsive_gallery');
$bID = empty($_GET['bID']) ? 0 : intval($_GET['bID']);
$fsID = empty($_GET['fsID']) ? 0 : intval($_GET['fsID']);
//Load the primary database record for the given bID
Loader::model('block');
//<--need this in 5.6+ (otherwise the new autoloader can't find the BlockRecord class)
$block = new BlockRecord('btSortableResponsiveGallery');
$block->Load("bID={$bID}");
//Loads empty object if bID=0
//Retrieve sorted images from our custom table if a block record exists and its fsID matches the fsID passed here...
if ($block && $block->fsID == $fsID) {
    $sg = new SortableResponsiveGallery($bID);
    $images = $sg->getPermittedImages();
} else {
    //Retrieve unsorted images from the fileset if this is a new block or the fsID's don't match...
    $images = SortableResponsiveGallery::getUnsortedPermittedFilesetImages($fsID);
}
//Render the images
Loader::packageElement('thumbnail_items', 'sortable_responsive_gallery', array('images' => $images));
exit;