The only thing holding up the dollar is an almost universal acceptance of it as a token of exchange.
If there is any kind of move away from that paradigm, it will plummet. Whether it plummets against other currencies or commodities is irrelevant.
You are absolutely correct. But as more and more countries begin to diversify their currency reserves, the dollar will fall further and further out of favor. Just look at all the countries that are considering the Euro.