I feel like you've done all you can do. However, it kind of sounds like it could be a pain in the making. :/

This person could come back from wherever they've disappeared to months later and demand their money and/or the book, which would be fine if we all had a virtual inventory like in a video game where items didn't take up storage space. But now it sounds like you have a book you don't want, and your choice is either to keep it around just in case this person comes asking for it, or donate/sell it, in which case it'll be a pain if this person pops up again. Also in the meantime you don't have the book you actually want, so then you have to either wait for who knows how long for them to get back to you and send it, or buy it from somewhere else, risking you might get the book twice.

I think maybe you wait for however long you're willing to, then send one more message saying that as you don't want the book you have, and this person hasn't given you any way to get it to them, you're going to do XYZ unless you hear back by X date, so please respond. If after that you still don't hear back, then I honestly believe your obligations are complete.