As ordered by divine law, if the Hebrews perceived Ezekiel's prophecy to have failed or for Ezekiel to have received revelation of God to admitting a failure, then Ezekiel would sooner have lost his title as prophet (Dt 18:21-22) and his book would obviously have had a very hard time being canonized.
In the prophecy, it said “she will become spoil for the nations.” (Ezekiel 26:5) This is relevant because Nebuchadnezzar did not receive any such spoils (Ezekiel 29:20).
But so what? Tyre being prophesied to become the “spoil of the nations” does not require that every nation get her spoils. Tyre has in every way become the “spoil of the nations” without Nebuchadnezzar being one of said nations. The nations attacking with Alexander received spoils in excess.
But wait, it is false that God's rewarding someone implies that a reward was originally promised them. This is odd. *There is no indication in the text to suggest that God's decision to gracefully reward Nebuchadnezzar stemmed out of a failure of the prophecy. Instead, the motivation was explicitly different: “I have given him the land of Egypt for his labor which he performed, because they acted for Me” (29:20)