on chart level you can add this calculated dimension:
=If(Match([Audit Status], 'Visit Completed', 'Draft Report Issued', 'Responses Due', 'Final Report'), 'Completed', 'To Do')
and leave your measure as it is.
However I would recommend to precalculate this in script and then use that field as a regular dimensions in your chart, because calculated dimensions tend to be performance heave on larger datasets (not sure about the amount of data you're working with).
Hope this helps.