Can a single DC be demoted?

Solution 1:

Yes, demoting your sole DC is allowable, and it will make your domain disappear and you'll need to make new users and groups in a new domain, and join your workstations to the new domain, if that's what you choose to do.

Anything that had a security principal assigned to it will also need to be assigned to the new security principals - eg if you have a fileshare right now with limited access, those user or group SIDs that have access will be gone, so you'll need to reassign to the new groups/users that you'll be creating.

You may want to see if you can temporarily add a second DC to your domain so that you don't lose the domain itself. I think that WSE will allow this, but I'm not that experienced with it. Search for that terminology (or work with your MS support staff on your ticket), stop searching for PDC and BDC unless you're hand-to-god working with NT 4.0 or older.

Edit - Aha - yes, you're incorrect about not allowing additional DCs in a WSE domain. You're restricted by licensing to not having more than one WSE in a domain (for longer than the 21-day grace period for a data migration) but you can certainly add a second DC on a non-WSE SKU of Windows server. And you should.

https://social.technet.microsoft.com/Forums/office/en-US/710863c6-e3ca-4526-9a65-569b5374f47d/windows-server-2016-essentials-domain-controller-replica?forum=ws16essentials