As I understand correctly If you have some kind of button that close the popup and you need a function that is triggered after close.

(function($) {

  $.fn.somePlugin = function(options) {

    // do some stuff with popup

    $('#closeButton').click(function(e) {

      //close popup

      if (options.onAfterClose !== undefined) {

         options.onAfterClose(e);

      }

    });

  };

})(jQuery);

it just pass the event from click event.

$('#someId').somePlugin({

    onAfterClose: function(e) {

        alert('after close');

    }

});