Before you delete a case where an eSignature has been requested, there should be warning message to Cancel the Signature request so that the form doesn't get stuck in limbo. Once the form is awaiting signatures, it cannot be edited or deleted from the Documents on the Admin side.
For Live cases, they show in the eSignature widget on the Case Listing page but deleted cases do not. If there are a lot of deleted cases, it would take forever to restore and find the case that's awaiting signatures for the document needing to be edited.