I'm trying to figure out if it's possible to determine what DC/GC you are talking to without using a sniffer.  I know you can check what logon server you authenticated against by using the set command but what I'm particularly interested in is say the DC you are authenticating against goes down and there isn't another available DC in the same site and the client is forced to communicate to another site.  Is there a command to reflect this status?

Curious.  Any suggestions?

The SET command isn't the proper way to check what domain controller you are currently using. Here is the proper way:

nltest /DsGetDc:<FQDN of your domain>

If you add the /force it will also force the rediscovery and pick another domain controller if the one which has been previously selected isn't available anymore.