Today, not even the staunchest fundamentalist would dare claim that all copies and translations of the Bible have been divinely protected from error. After losing this decisive battle, the defenders of inerrancy retreated to the only high ground left for them. They found refuge in claiming that at least the original autographs of the Bible were inspired of God and so by necessity inerrant. Since none of the original autographs had survived the passing of the centuries, perhaps the inerrancy advocates thought that they had at last set up an impenetrable line of defense. The fallacy in this line of reasoning should be obvious to anyone who has even rudimentary skills in critical thinking.
Logicians call it the argument from ignorance.
The fact that one cannot disprove an assertion does not prove the truth of the assertion, since the absence of negative evidence by itself is never conclusive positive evidence. One could just as well argue that a failure to disprove the existence of elves must mean that elves do exist, and with that kind of logic one could prove just about any fantastic claim. This often ignored principle obligates the claimant of a proposition to prove that his claim is true. The challenger of the proposition is under no obligation to prove that it is not true. Accordingly, the one who claims that inerrant autographs of the Bible once existed is obligated to prove that they did indeed exist.