Hey @jeffatpresence,
Thank you for your question. While the historical data will be retained, you can only call the API successfully if the user that is calling the API currently has a webinar license applied. You can check if a user has a Webinar license using the feature.webinar property returned by the Get User Settings API.
You can also apply a webinar license to a user with the API but I understand that this may not be something you want to do on another account.
Thanks,
Max