Is it possible to restore/reactivated a deleted Organization in CA Risk Authentication?
No, it is not possible to restore/reactivate a deleted organization.
LDAP based Organization you should be able to restore/reactivate them by modifying the database directly.
Update "ARUDSORGANIZATION" table of CA AA database. Change the "STATUS" to "1" for the deleted organization.
I haven't tested this functionality ( AA 8.X onwards) on organization hosted on CA database.