Well, getting beyond the reality that the earth never noticed a global earth surface covering flood of water in the last 800,000 or so years; or shall we bend the spoon? Nothing, absolutely nothing, supports the notion outside of fairy tales.
Ok, that said...notions of 're-introduced writing systems' is purely and un-evidenced speculation. Secondly, what makes you think Shandi was about monotheism? Of course many think the roots of Yahweh weren't monotheistic either, so then they would have something in common. You might as well ask 'What if Loki is the real God, and he gets his socks off by playing differing gods to differing people over the ages and watching the cacophony?'. That would fit the evidence better than the God-breathed world of the Bible. Nothing suggests the Hebrew theistic roots have any ties to the Chinese.
https://en.wikipedia.org/wiki/Shangdi
The earliest references to Shangdi are found in oracle bone inscriptions of the Shang Dynasty in the 2nd millennium BC, although the later work Classic of History claims yearly sacrifices were made to him by Emperor Shun, even before the Xia Dynasty.
Shangdi was regarded as the ultimate spiritual power by the ruling elite of the Huaxia during the Shang dynasty: he was believed to control victory in battle, success or failure of harvests, weather conditions such as the floods of the Yellow River, and the fate of the kingdom. Shangdi seems to have ruled a hierarchy of other gods controlling nature, as well as the spirits of the deceased.