ADT - 3 Filing

ADT-3 should've been filed before he surrendered his membership. It is no longer possible. Further ADT-3 is mandatory as a proof of resignation both for the auditor and Company's records. 

But since he no longer has membership with ICAI, you can go ahead with filing ADT-1 for new auditor after obtaining declaration from previous auditor, is my view.

However as this is a unique case, please also obtain guidance from MCA by raising a ticket if this is not a hypothetical issue.