int export KilledNotify_hook(int ID)
{
  string port = ReadInfo("_notifyport", ID);
  if(strlen(port)) {
    ARexxSend(port, "!"); /* just send anything, don't wait for reply! */
  }
}

ConstructInfo("_notifyport", "", "", "LS", "", 0, 0);
Hook("BufferKill", "KilledNotify_hook");