Nice way to enforce business rules on several tables into one rule.
It is also impossible to make an office active when the region is inactive.
My way would be to use an UPDATE-trigger on region and office.
The region version:
CREATE TRIGGER dbo.TR_InvalidRegionIsInactiveButOfficeIsActive ON dbo.Region FOR UPDATE
IF EXISTS (
INNER JOIN dbo.Office
ON Inserted.RegionId = dbo.Office.RegionId
WHERE Inserted.IsActive = Convert(bit, 0)
AND dbo.Office.IsActive = Convert(bit, 1)
RAISERROR ('Cannot disactivate Region with an active Office', 16, 1)
The trigger on office would be of a similar structure.
This will give you the opportunity to issue a more descriptive error message.