Brock wipes out Cena leading to a DQ win (plays into conquering Cena) via excessive force or Brock getting a countout win then putting Cena into the ring and standing guard as Rollins cashes in to win the title.
Allows Cena to go away and keeps the belt on TV. Brock is still a heartless monster and unstoppable force. Authority regains control of the belt.
Seems to check a lot of boxes…
I just don't see Rollins as the guy who's going to get that belt, but I wouldn't bet against your scenario occurring on Sunday in the least. Should that happen, though, Cena's getting that title back IMMEDIATELY, so I wouldn't be hoping for it if you're a Rollins fan. Business is in the toilet and there's no way they're running with anything but their guy on top.