Johnny,
Of course they would have to honor it. That is not your problem anymore if SB go down.. The book accepted your payment, therefore, you are good now. You can just request your cash via FEDEX if you want now. It now becomes the books problem if SB is finished.
If a book pays you 24 dimes via NETeller, and NETeller folds, after the book sent it. Do you go back to the book and tell them NETeller stiffed you, so you want them to pay you another 24 dimes LOL. They'd laugh at you... I wouldn't worry Johnny baby, you are ok now..