The Ch. 48 page-16 save-then-kill rule (Sanji Save Then Kill Doctrine) was articulated to Gin in dialogue. The Ch. 60 chapter is the enactment — both fighters acknowledge the doctrine and apologize in advance. The mercy-recipient-must-kill-mercy-giver combat-grammar lands as a mutual apology (Gin’s “the best I can offer” / Sanji’s “Thank you” / Gin’s “Sorry” / Sanji’s “You small-fry scoundrel”).
Forward-payoff
The Ch. 67-68 combat-resolution. The contract installed in Ch. 60 will be broken at the moment of the killing-blow — Gin refuses (the contract-break-from-Gin’s-side) and Sanji’s response is to not retaliate (the contract-break-from-Sanji’s-side). The arc’s payoff is both fighters refuse the contract simultaneously, leaving Krieg as the only honor-detesting party on the battlefield.