This whole house of card is very modern, there was no such thing as "Reserve currency" not even the British pound, it was the most traded currency. but holding a currency's (debt) as a foreign reserve instead of gold is very recent phenomena, even central banks reserves or their function is also rather modern phenomena.

while Yuan usage in trade will reduce the US influence, the amount of assets held in dollar nominated investments is so so much bigger, and this will very slowly change if it will at all.