AJAX response, edit tags

Wait for WordPress 4.7 on 6th December. It has this almost built-in.

If I got it right, then you’ll want to prevent some terms from deletion.
I already made a snippet for that which works with WP 4.7

add_filter(
  'user_has_cap',
  function ( $allcaps, $caps, $args ) {
    if ( ! isset( $args[0] ) || 'delete_term' != $args[0] ) {
      // not the deletion process => ignore
      return $allcaps;
    }

    $term = get_term( $args[2] );

    // HERE YOU'LL LIKE TO PUT YOUR LOGIC INSTEAD OF THIS:
    if ( $term->count <= 0 ) {
      return $allcaps;
    }

    // for all other cases => reject deletion
    return [ ];
  },
  10,
  3
);

For more details read https://wp-includes.org/536/capabilities-taxonomies-terms/#Preventnon-empty_categories_from_deletion