There are two kinds of originals to the Book of Abraham:
(1) The original book that Abraham wrote.
(2) The original that was in the hands of Joseph Smith.
Factually, they are not the same thing.
Abraham wrote a book in ancient times. This is not a piece of fiction. This book was written by his own hand, as Joseph Smith claimed. Contrary, however, to Joseph Smith's assumptions, Joseph Smith never had a copy of this, or the original of this in his possession. It disappeared in ancient times.
So, when I say there is no "missing papyrus," I am NOT saying that there never was an original that Abraham wrote in his own hand. What I am saying is, that particular book was never physically available in modern times. It was lost to antiquity, or was hidden up, as were all the copies of it. One or the other.
Joseph Smith had a papyrus that he worked with, which was instrumental in the translation of the Book of Abraham. This papyrus is not the same as the book that Abraham wrote in ancient times. Nevertheless, it is the Book of Abraham because of the way people used it anciently. The characters in it were used to represent things in the Book of Abraham. Therefore, there is no "missing papyrus" in the sense that the papyrus that Joseph Smith used to translate the Book of Abraham is available. The "original" that Joseph Smith had, is available. The "original" book that Abraham wrote in ancient times is not available, and never was in modern times.
This is why, when I say I am against the missing papyrus theory, what I really mean is, I am against the idea that there is some papyrus that we don't have that Joseph Smith had. I am not saying that Abraham did not write a book in ancient times in his own hand.