Schema Extension and Rollback - Windows 2000 to Windows 2003 AD Upgrade

The situation is we are doing a Windows 2000 to Windows 2003 AD Upgrade covering multiple sites and domain structure is Parent Domain ( and Child Domain (  Our goal ultimately is to upgrade the AD 2000 to 2003 in mixed mode first then migrate all Exchange 2000 servers to Exchange 2003 from the child to the parent domain then collapse the child domain.  

My question has to do with schema extension rollback.  Since our plan includes just upgrading the AD 2000 to 2003 first, we are going to run ADprep /forestprep & ADprep /domainprep - thus extending the schema and replicated to all sites and both domains (Parent & Child) then introduce the new Windows 2003 server as a DC in the parent domain where all the 5 FSMO roles are located.

As a recovery strategy - in the main site where the first part of the AD upgrade will occur, we are breaking the Raid 1 mirror on all the Domain Controller (before running ADprep) - just in case something happens to the upgrade, we could rollback the fastest simply by just plugging out the other mirrored drive (with the extended schema) and plug in the one we took out that holds that Windows 2000 AD (with the unextended schema) and we should be back in business (supposedly).

The thing is, we will not be touching other sites that also has DCs that are also Global Catalog servers (we won't break the Raid 1 mirror there).  What we have in mind is - if a problem occur once the schema gets extended and replicated to all sites, we fix the main site by plugging in the Windows 2000 AD drive and regarding the others DCs found on the other sites what we do is - uncheck the Global Catalog server (AD Sites & Services MMC) then recheck it - that in a way should supposedly erase all AD attributes and schema on that particular DC and once GC is check, the AD attributes and schema should replicate coming from the main site holding the AD 2000 attributes and Schema.

What is the flaw here?  Please tell me why it should not work as a form of rollback once the schema gets extended.   We don't have a backup mechanism in place.

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i suggest to do a ntbackup (all files/drives + systemstate) to another server(share).
so you can do a full restore, or only a authorative AD restore (what is, what you want :)
i would not break the mirror and use it as a fallback solution.
all your GC's and SubDomain DC's will be confused.
maybe if you move all Forest FSMO Roles to the subdomain, but i don't know if this is possible.

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