Zeus is being patronizing: He doesn't grok that Diana holds him to be a murderer, thinking instead that she's feeling something like he would if Hera stomped on one of his mortal lovers; he didn't have faith in Diana's diplomatic skill and expected the fight would only end in death; he would prefer the death of an avowed and powerful enemy to that of a delinquent servant.
Zeus remember Athena's fondness for Diana. I don't know if he ever find out that reports of her death were greatly exaggerated, which has a strong influence on how likely this is to influence him.