I am afraid that for a full answer to this question you will need to talk to your certification body, because AS9100 gives you the requirements on how to create an aerospace QMS, but it does not tell you how to audit it. Even ISO 19011, the guidelines for management system auditing, does not go into this sort of detail. The standard gives you the information on how to create the processes, which processes are needed, and some of the requirements they need to meet; but not how to assess these processes when a company has not had aerospace customers for a while. It also does not talk about if you do or do not have customers.
That being said, documented records are not the only information used to audit the processes of the QMS. You may be able to assess the processes through interview where records do not exist because there have been no customers. It can be enough to know that the processes are in palce, understood, and ready for when a customer returns.
You can learn a bit more on how the certification audit works in the article: What to expect at the ISO certification audit: What the auditor can and cannot do, https://info.advisera.com/free-download/what-to-expect-at-the-iso-certification-audit