If they had a word disabled for low CTR, they would delete the word, save changes to the AdGroup, then readd the word and save changes.
Or they would delete the word, make a new campaign or AdGroup for the word.
In both cases, the KW is no longer shown for searches, and gathers 0 impressions. However, there is no 'restore full delivery' or any way to have the word shown again.
Either this is a bug in the G system, or the words are flagged by G as low CTR, and now shown. In either case, how do you get these words to once again gather impressions?