I don't think they necessarily booked themselves into a corner where they had to resign Brock. If they really put over Reigns strong on Sunday, then on some level that would have transferred at least some of the value of Brock beating taker and his reign onto Reigns. Hell, they could have had Taker come out to "pass the torch" after the match and bring it all full circle. It wouldn't have been perfect, but it would have at least partially worked.