The last of the passages have been cleared to the best of my abilities. Three are utterly impassable. The weakness in the roofing of the main chamber seems to have been a flaw in the architecture of the entire tomb. The one passage that has not collapsed lead to a long, shallow set of stairs that ascend to the surface at a point just beyond the edge of the desert. Over this entrance is a high pillar, perhaps a marker for this site so that those who wish to pay tribute to whomever is buried here might more easily find it.
I have found no clues that might help me in the translation of the writings I have found, and I have exhausted all avenues of investigation at this site (bar, of course, the sarcophagus, which I have no intention of trying to open at this time).
I am going to return to the Lighthouse and begin construction of a library on the nearby island. Once I bring in a few books on languages, I can attempt to translate the writings on my own.