We lost this perk once before and got it back, so I'm hopeful although not optimistic.
There are two ironies for me:
The first is that I'd use this option mostly for books that didn't seem worth a credit. I'll choose to read them instead, now, so those will be purchases not made.
The bigger irony is that for the last nine months, my credits (free or nearly so) have cost
less than the Whispersync price on the books I purchased after borrowing them from OverDrive.
In fact, I can understand Audible's (Amazon) wanting to rationalize its price structure. But I've got an ample library of unheard Audible books and what with free audiobooks at OverDrive, it could be a very long time before my pent-up demand translates into my becoming a full-price for credits customer again. This will mostly affect impulse purchases and impulses don't last.