There are three known instances of this happening, one resulting in a death.
Rose swallowed a macadamia nut shell, which started a domino chain of health complications that ultimately led to her death. The surgery to remove the shell was successful, but she passed shortly after due to the other issues.
Beans swallowed a piece of a blanket, needed surgery to get it removed, and has since fully recovered and seems to be doing fine now.
Demeter swallowed a
piece of earbud foam 🄰 and similarly had it successfully removed.
In any case, they do have a real vet they send the ferrets to in case shit happens.