Hi there Matais,
Depending on the situation an e-mail to Apple may help you. I had a similar issue where I had accidently deleted one of the 'parts' of my audiobook and was unable to retrieve it. I used the "Express Lane" feature on the Apple website, which essentially involved filling in a short form on what the issue was. I received a reply within about 18 hours saying that a new copy had been placed in the 'downloads' section of my iTunes ready for me to download! Problem solved! I'm not sure if the response will differ if you wilfully deleted your audiobooks as it says you cannot redownload audiobooks somewhere in the iTunes Store terms and conditions.
Nonetheless, I'd definitely say it's worth a go. Safe to say I am very pleased as I thought I was going to have to shell out another £17 to finish listening to the story!
I hope this is of some help to you (or anyone else who may have this problem)!