The knowledge of how to read ancient Egyptian hieroglyphs was lost. It was not until the early 19th century, with Jean-François Champollion's deciphering of the Rosetta Stone, that scholars could begin to understand these ancient writings. The Pyramid Texts themselves were first discovered in 1881, and translations into European languages followed, with an English translation by Samuel A. B. Mercer becoming available in 1952.

The direct evidence and scholarly theory of this specific ancient Egyptian belief could only be formulated after the discovery and translation of the Pyramid Texts in the late 19th and early 20th centuries. It is through the modern study of these ancient texts that the belief of the sky weeping for a dead pharaoh was confirmed.

44:29 is most likely now part of the long list of Quranic miracles and prophecies, and any official attempt on your end to verify and document this would be heavily appreciated.

May Allah bless and reward you,