I only have a layman's knowledge of this part of history, but this strikes me as unlikely. Surely something was known of him for some time in other sources, probably hundreds of years at least, before those source were also lost? The loss of knowledge is also second-order: we have lost knowledge of what was known to our predecessors.
Still, the end of Mesopotamian records is abrupt. There's a written record from prehistory until the wars of around 700 BC, where the use of writing drops off but doesn't completely stop. But written records in Akkadian, the education of priests and scribes in Akkadian and Sumerian (itself dead for 2000 years by then as a purely liturgical language) basically stops after the fall of Babylon in 539 BC.
I'd note that writing in antiquity was deeply tied to both administration and to religion. The Persians were Zoroastrians; they do not seem to have oppressed, but state support went to Zoroastrianism and not the traditional Mesopotamian cults (and their scribes and schools). They imposed their own administrative structure on the conquered territories. Persian became the written standard, pretty much overnight. Akkadian seems to have ceased to be spoken within a couple generations among the ruling class, and within a few hundred more years it was not only dead but basically forgotten.
This probably isn't so much a move away from the use of writing, but a shift away from Akkadian cuneiform on clay tablets to Aramaic on vellum. Clay tablets, even unfired, survive a long time. Vellum doesn't in that climate.
[1]: https://youtu.be/cq1g8czIBJY [2]: https://youtu.be/Qr4FiT0ks7I
If you find yourself in Chicago, you can see carved stone reliefs and a lamassu from the palace at Dur-Sharrukin at the Oriental Institute Museum at the University of Chicago.
If you’re talking about the recent Syrian war, Ive read there’s reason for optimism.
Many of the ancient fortress were used by fighters, not necessarily to defend against attack. More to keep prisoner, train, etc.
But what I read was about medieval Kracs, which are still functioning fortresses, not ancient Mesopotamian structures.
I met a traveller from an antique land
Who said: Two vast and trunkless legs of stone
Stand in the desart. Near them, on the sand,
Half sunk, a shattered visage lies, whose frown,
And wrinkled lip, and sneer of cold command,
Tell that its sculptor well those passions read
Which yet survive, stamped on these lifeless things,
The hand that mocked them and the heart that fed:
And on the pedestal these words appear:
"My name is Ozymandias, king of kings:
Look on my works, ye Mighty, and despair!"
Nothing beside remains. Round the decay
Of that colossal wreck, boundless and bare
The lone and level sands stretch far away.
— Percy Shelley, *Ozymandias*
Sargon II was king of Assyria, ruling from 722 BC until death in battle in 702 BC. He almost completely reunified Assyria in the then millennia-old tradition of grand empire-building in the region. His assumed name Sargon was appropriate; Sargon I, Sargon the Great, was the first to have created a unified empire in Mesopotamia, nearly two thousand years earlier. The records of Sargon the Great's exploits were still around to read, and people could still read them. Although he was near-mythical by then, like Gilgamesh. The subsequent wars Sargon II's empire-building led to would effectively destroy the Mesopotamian political-economic system and leave it ripe for external conquest, first by Persians, and then Greeks, effectively bringing that 3000 year old civilization to a whimpering end over the next couple hundred years.
His name was actually more like Sharrukin, or Sarrukin, in the Akkadian language. We call him Sargon II because that is the Greek version of the name recorded in the Bible and transmitted in the Western canon. He is mentioned only once, in passing, in the Book of Isiah. That single passing reference to him as King of Assyria, was everything that was known of him for 2500 years, until the ruins of Dur-Sharrukin, his capital (destroyed during the mentioned wars) were excavated in the 19th century. Only the faintest echoes of the very last stages of Mesopotamia survived through the transmission of Western/Persian/Islamic civilization. Faded memories several generations old, by the time the earliest Greek and Jewish authors started writing things down. Like you say, it's a good thing clay lasts.