On the Merchant Performance screen, deactivated merchants are also shown (and this is fair enough), however I have a suggestion for an additional column, to show whether or not a particular merchant is currently active or not.

I sometimes use this screen to double check that I've correctly entered the merchant information into my own database - if I've got zero impressions / clicks then there must be something wrong at my end - but this is perfectly reasonable if the merchant is no longer active - in which case I don't have to do anything.