You wrote: "note also the last line of the inscription, which is a prayer that the person's nephesh will be bound up into eternal life." That is not correct: the word used in the (abbreviation given on) the last Hebrew line (נשמתו) refers to the "neshama," and not to the "nefesh."
However, in the Hebrew text of 1 Samuel 25:29, on which this line is based, the word
nephesh is indeed used.
In either case, though, it expresses the biblical belief in life after death, which is the point.