(There was none who sold himself to do what was evil in the sight of the LORD like Ahab, whom Jezebel his wife incited. He acted very abominably in going after idols, as the Amorites had done, whom the LORD cast out before the people of Israel.) …"Have you seen how Ahab has humbled himself before me? Because he has humbled himself before me, I will not bring the disaster in his days; but in his son's days I will bring the disaster upon his house." - 1 Kings 21:25-26, 29 (ESV)
Ahab was sold-out; not to God but to doing evil. Even the most wicked, evil person is not beyond the Lord's grace and mercy. God spared Ahab from his pronouncement because Ahab repented. While Ahab's conduct is so reprehensible, the Lord's conduct is incredibly so merciful.