Elijah once again confronts Ahab, this time about the death of Naboth even though it was Jezebel who arranged the murder. Ahab is being judged by God not only for this act but for his overall rule and lifestyle. The heads of state (and households) are responsible as priests, prophets and providers for their families.
God's judgement is always wrapped in His grace and mercy. Even in His judgement of us, He allowed us space and time to repent before Him.
Ahab appears to be remorseful, but is it genuine repentance? Did he return to his wicked ways? And as we see in Ch. 22, he is killed and licked by dogs just as God said he would be.