Typically, when an anonymous user manually saves a transaction, the user sees a dialog with a prompt to provide a challenge phrase (based on design) and a transaction reference, both of which are required to retrieve the transaction in another session.
If the anonymous user has never manually saved, and background save is activated, how does the user retrieve the transaction after an unexpected exit of the form?
Some point of contact would need to be added to the workflow. Does the user know where to access the form? is there a portal? is a job controller used for the workflow?
I would be inclined to recommend injecting an email service in the workflow for example on the Form saved processor service to send an email the first time background save fires. The form would need to capture an email address.