If lost or destroyed, a new copy can be obtained from the Archaeological expert. After the quest you can also find it in the bookcase in your Player-Owned House made through Construction.
Below is the text you can read from within the book.
This is a rough translation of the stone tablet brought to me by courier earlier today. The cuneiforms of this particular tablet are far different to anything I have previously seen in my career as an archaeological expert.
Where possible I have given as accurate a translation as possible, but some of the words I have attempted to translate hold different meanings depending upon their intonation and context; Due to my unfamiliarity with this language, I have given possible translations for these words wherever I have encountered them. Wherever I have a word in brackets, it is a word which has many meanings depending on the context, although the general meaning should be clear to even a casual study.
Hopefully this translation will help you in your excavations Asgarnia, and as usual I look forward to seeing what relics you bring back to the Museum of Varrock this time! Your friend, as always, Terry Balando
...the permanent (exile/journey) of the people ended. And so it came to pass, that deep in the (fiery/uncomfortable) desert, the gods (argued/decided) amongst themselves that the (fortress/home) would be the (selected/chosen) place that would (imprison/conceal) the (wealth/power). Thus (guarded/protected) by the (unusually archaic word here, I believe it means either the sick or the dead depending on the context) and (defended/trapped) by the (diamonds/crystals) of (this word is untranslatable). So it was that the gods left the four (diamonds/crystals) as the (key/secret). (Guarded/Protected) by the (again, this word has no modern equivalent) and held by the (worthy/strong) so that the (wealth/power) might forever be (imprisoned/concealed). There seems to be some further missing information continued onto a further tablet, but from this preliminary translation I think you may be onto something very big indeed!