I think it is becoming fragmented
Discussion
I think they dont have a plan to replace it yet.
It's already been happening. Trade in real, rinminbi, rubles, rands or rupees.
Russia reduced its dollar reserves (and even paid Trump in cold hard dollar currency in a briefcase for refueling the plane in Alaska which was hilarious because they're banned from the dollar access)
China has been severely reducing it's dollar reserves, and I guess after the whole India thing, the Indians are reducing that reserve currency as well.
Demand has dropped significantly