Hyper-V Server - Can't UnJoin An Orphaned Domain

I have a Hyper-V host running on a Windows 2008 server that does not have a desktop GUI.

This server is currently joined to a domain that no longer exists and there are no domain controller for that old domain still on the network.

Using a local admin account, at the windows command prompt, I'm trying to unjoin from the non existing domain.

I've tried this command:

netdom remove /d:DomainThatNoLongerExist.COM HYPERVComputerName

I get this:

The specified domain either does not exist or could not be contacted.

The command failed to complete successfully.

Instead of "unjoining first", I've tried just joining to the new existing domain, but each time I try, it says it is already joined, but it really isn't already joined; because the name of the new domain is a subdomain of the previous domain, it assumes it is already joined, and that false presumption is causing me a lot trouble.

So, can someone please tell me how I can un-join this non-longer-existing domain?

BTW, this especially important because I can't access any of the currently running virtual machines via Hyper-V manager because it automatically authenticates using the client's windows-login-credentials which are for another domain than the hyper-v host's non-existing domain. The only access I have is a local admin account, and I cannot figure out how to use those credentials in Hyper-V Manager from a remote machine (and I know no way to launch Hyper-V Manager on the Host machine after logging in as a local admin).