A second Ruiz win would spark immediate talk of him facing WBC champion Deontay Wilder, who is due to meet Tyson Fury for a second time in February.
Wilder and Ruiz share the same advisor, so boxing could, in theory, be within touching distance of a first ever bout for all four heavyweight belts.
There is no rematch option in the contract this time, so were Joshua to win, he too could look to Fury or Wilder to set up a captivating 2020 in the glamour division.
On the other hand, a second loss would limit Joshua’s options in the short term and undoubtedly produce calls for him to hang up his gloves.
Even in defeat, that would seem a harsh verdict on a man who has achieved so much in so little time.
But Costello concludes: “It will be a long, long way back.”
Tyson will be ringside. So will Joshua be better or destroyed?