Hello all,
Well, I did it. The Management History Migration Wizard took 49 hours to assess and move 3.75 million change history items from a 94 GB ARS 6.5 database (there's your datapoint, Sargay 
)
To get the full gory details, see my blog post: http://arsdears.wordpress.com/2013/02/12/activeroles-server-management-history-migration-wizard-a-personal-experience/
The history itself got moved; the edsvaDeprovisionReportXML attribute is populated for those "problem" User objects, and the attribute changes not contained in that are reflected in the surrounding Change History items.
edsvaDeprovisionReportXML contains the changes to the following attributes:
description
displayname
edsaAccountIsDisabled
msExchHideFromAddressLists
altRecipient
showInAddressBook
edsaMailboxSecurityDescriptor
but not
authOrig
manager
homeDirectory
accountExpires
These last four are under the username of the ARS service account; the depro itself takes place under the username of the admin who initiated the depro request.
However, the problem users who were deprovisioned in ARS 6.5 still do not have the "Undo Deprovision" option, but the "Deprovision" option. The edsvaDeprovisionCommands is 1, and edsvaDeprovisionStatus and edsvaUndeprovisionCommand are unpopulated. By contrast, a user deprovisioned in ARS 6.7 has the following attribute values:
edsvaDeprovisionCommands:2
edsvaDeprovisionStatus: 1
edsvaUnDeprovisionCommand: 1
How do I get the Deprovision-related attributes populated? If there is no way to do this, then has anyone else found a way to deal with these inconsistent deprovisionings?
Thanks for any ideas you guys have!