Further to that, I did read at Sailing Scuttlebutt (sorry, no link) that the current protocol has a provision that if the CoR was eliminated, the next challenger would become CoR. So...I guess it's down to the fine print if "quit" qualifies as "eliminated".

That article also alluded that Sir Russel wanted Artemis to be the CoR but that Ellison chose Australia (not that that every officially happens since the Defender doesn't officially "choose" a challenger...but some VIP regularly just happens to be on the observation boat with the new Defender the second their boat wins the event to become the CoR).