Yes, if the book goes lost after 26 days and was WL you will get the credit back and go back to same place on the WL. If it was FIFO then it's going to your reminder list and you can order the next copy.  But the advice is to wait or check with the sender (make sure they actually mailed and not just marked it mailed and forgot, etc.) so you don't get two copies. From the help docs:

A book I requested is lost in the mail. What now?

• If a book you requested does not arrive by the 26th day (the 35th day if the sender or requestor is outside the contiguous US) after it was marked mailed, it will be declared lost in the mail at PBS. The requestor does not mark the book Lost; the system does this. 

The requestor will get credit back, and the book will go onto the Wish List (if there are no available copies in the system) or the Reminder List (if there are other copies available to request).  If the book was a Wish List book when it was requested before, the requestor will go back to his or her previous place "in line" for the book.

What to do if a book is declared "lost" en route to you:

• If you are at an address outside the contiguous US, OR the book was coming from an address outside the contiguous US, read  If you are sending or requesting a book from/to outside the continental/contiguous US.... Also follow the rest of the instructions below.

No matter what the orgination or destination address of the book, follow the instructions below:

• Check with the sender about the mailing date (in case it got mailed late or there was a problem with mailing) -- you can use the PM button on the "lost" transaction in your Transaction Archive to send the message
  • If the mailing was not delayed, the sender can call 800-ASK-USPS and supply the tracking # for the package [or in the case of suspected mail theft, call 1-877-876-2455 or go to https://www.uspis.gov/ (the Postal Inspection Service's website)] .
  • This will help USPS try to recover the book if it truly has been lost in the mail/misdelivered.
• Don't re-request the book for at least 2 weeks, unless you are willing to run the risk of getting two copies (and paying a credit for both). Members outside the contiguous US should wait longer, depending on their typical transit times.
  • If this is a Wish List book, you should put the Wish on hold while you are waiting, so you don't end up with 2 copie of the book.
  • If you do end up getting 2 copies of the book because you re-ordered within 2 weeks after it went "lost"
    • You must mark both copies received - Mark the "lost" book received from your Transaction Archive as described in I received a book that was 'lost in the mail'
    • The only exception to this is the situation when the "lost" book was actually mailed very late without notice from the sender - if this is the situation AND the requestor has re-requested and gotten a second copy, the requestor does not have to mark the late-mailed book as received.
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