Jonah 2
4 And Jonah began to enter into the city a day's journey, and he cried, and said, Yet forty days, and Nineveh shall be overthrown (Not "if" you don't repent).
5 So the people of Nineveh believed God (They believed God was going to overthrow them), and proclaimed a fast, and put on sackcloth, from the greatest of them even to the least of them.
6 For word came unto the king of Nineveh, and he arose from his throne, and he laid his robe from him, and covered him with sackcloth, and sat in ashes.
7 And he caused it to be proclaimed and published through Nineveh by the decree of the king and his nobles, saying, Let neither man nor beast, herd nor flock, taste any thing: let them not feed, nor drink water:
8 But let man and beast be covered with sackcloth, and cry mightily unto God: yea, let them turn every one from his evil way, and from the violence that is in their hands.
9 Who can tell if God will turn and repent, and turn away from his fierce anger, that we perish not? (Why did Nineveh repent? They knew that God might have mercy on them and not overthrow them. It was their only way to be spared.)
10 And God saw their works, that they turned from their evil way; and God repented of the evil, that he had said that he would do unto them; and he did it not. (God saw that Nineveh repented at Jonah's preaching of destruction. God did not have to destroy them since they repented. Nineveh was Israel's enemy. God was only defending the promise seed of Genesis 3:15 as He has done throughout the OT. When Nineveh repented and was no longer a threat, God changed His mind. He did not have to destroy them.)
To say God knew ahead of time that Nineveh would believe the preaching of Jonah and repent, and He in turn would not destroy them, would make God out to be a liar. I'm not willing to do that or add to the preaching of the word to fit a theology.