Saudi only accepting oil undoubtedly started it, but even if they accepted other currencies now, I don't think it's going to matter too much. The US Dollar has already established itself as the reserve currency, and nearly every country has a huge stockpile of it. It's going to remain the most convenient option even without the petrdollar concept because it's going to remain globally accepted.

This doesn't mean that the USD can't collapse, but rather that it's a strong, liquid currency. Strictly speaking, it's still not backed by anything at the end of the day. Saying it's backed by oil is almost like saying Bitcoin is backed by whales IMO.