How to strip html comments plus all tags inside it?
This is what theme_closure() does (in theme.inc):

function theme_closure($main = 0) {
  $footer = module_invoke_all('footer', $main);
  return implode("\n", $footer) . drupal_get_js('footer');
}


which means it's going to ask every module to run its footer hook plus get all the js to be put in the footer and return it:

$variables['closure'] = theme('closure');

to populate the closure variable.  So.... if you can't preg_replace() or regex() it out, why not just find what module is putting in there in the first place (seems pretty obvious) and kill it off there? 

EDIT/ADDITION:  IF it's a bug, fix it here, otherwise if it's just something you want different, preprocess it.  But it seems to me that a node status check might be in order in the module's footer hook.