From John Sander’s paper Be Wary of Ware:

God’s announcement to Hezekiah and Nineveh were stated in an unconditional/inviolable way. How do we know that they actually were not inviolable? Because what God said would happen did not happen. That is, it is only because they did not occur that we know that these seemingly “inviolable” predictions were, in fact, conditional upon what the human agents did. But what about seemingly “inviolable” predictions that did come to pass? Were some, even most of them, actually conditional upon the response of the human agents? The tendency is to think not, because they came to pass. However, I believe that there are actually very few such “inviolable” predictions.