Charles gave an excellent explanation of why the US dollar could still be used as a world reserve even if it isn't used for the trading of oil. As a point of reference, Wikipedia is saying that the US dollar makes up about 50% of the worlds foreign exchange reserves as of Q4 2016. https://en.wikipedia.org/wiki/List_of_countries_by_foreign-exchange_reserves#Currency_Composition_of_Foreign_Exchange_Reserves

And here is some even more updated information from the IMF.
http://data.imf.org/?sk=E6A5F467-C14B-4AA8-9F6D-5A09EC4E62A4

Rapid inflation in the US as a result of the foreign dollars coming back home can only happen if the worlds central banks are no longer holding them as reserves.

Thanks for this interview Dave.