AADDS: migrate AD from windows server DCs over to AADDS and then remove DCs
Mike Stephens commented
If you want to remove your domain controllers, then move to Azure Active Directory and go all in the cloud. Moving on-premises domain controllers to Azure AD Domain Service simply means you lifted your domain controllers to the cloud. You still have domain controllers. That is not the intent of Azure AD Domain Services. AAD DS is an extension AAD that provides support for legacy applications that use Kerberos, NTLM, LDAP, and other legacy protocols.
Senior Program Manager
Azure Fabric | Domain Services