I seem to be having a lot of these lately.  Anyway, I just had a wish list book go lost and PBS automatically gave me to the next person who had the book available.  I know many people say to wait a while since the book may turn up, but since this is a wish-list book, if I wait for it to turn up I will lose my place on the wish list.  I don't know of any way to turn it down and ask that I don't lose my place on the wish list in case it never shows up.

I'd just let the request go to the next person and if they both eventually show up you can repost one copy.  It's a WL book so you know somebody will want it. 

I suppose you could always contact PBS and have them cancel the order while placing you on hold at number one on the WL until you're sure you're not getting the lost book. You could then unhold the book on the WL and let an offer come through. I don't think there is any other way.

And when a wish list book does go lost, I try to get to my wish list right away to place the book on individual hold there until I know whether I want another order or not. But of course sometimes it can happen that I'm not fast enough. Both suggestions above could work for you, Kate.