It's certainly plausible, they would be comparable in size to the other empires of the the Early Iron Age middle east. As to what the results are? Hard to say, other than that you've butterflied the entire history of the Middle East and therefore the world.
It probably doesn't last super long, none of the Early Iron Age empires did. They'll fall apart, and the mantle will fall to another power. Might cycle back to the Hittites a few times, as simply sticking it out will probably ensure their culture sticks around for a few more centuries.
Their monopoly on iron will not last very long, that will only be a decisive edge for a little bit. '
Obvious change is that Greece is pulled into the eastern world much sooner, and its dark ages are cut short if it happens at all. Not sure what the impact of this is - the geography of Greece leads me to think that it will always be peripheral to some extent, and it will go down a similar path of development. Still, a more vigorous contact and exchange for such a long time is sure to have huge effects.
It will also butterfly Yahwism/Israelism/Hebraisim/Judaism as we know it. It's interesting to look at it look this: The central conflict of Israelite pre-History that probably led to its development was the conflict between the Hittites and the Egyptians in the land of Canaan. That being sustained could lead to the perpetuation of more ancient tendencies of the religion.