To login into the system without a password request you need to add remote machine public RSA key into the target machine ~/.ssh/authorized_keys Public key location: ~/.ssh/id_rsa.pub This is really useful for remote script execution under the requested credentials.
Every good administrator has a recovery plan. Every good windows AD administrator have got a valid backup of active directory database (backup made not later then your AD tombstone lifetime
This article describes the procedure of removing failed not restorable DC controller from the forest.
You should use this procedure ONLY if you are sure that you are deleting a DC that will never be available again.