Gene Drives Reversible?

NYTimes magazine has an article on gene drives, discussing the positives and negatives.  Lots of concerns about negatives, particularly outside the scientific community.

In reading it I wondered:  if I understand correctly, the gene drive consists of a genetic package which says: "if you find gene A, replace it with gene B and Crispr package X."  So a gene drive spreads a gene throughout the population while also spreading the Crispr package needed to replace A by B.

So what did I wonder?  Whether a gene drive isn't reversible, just do: "if you find gene B, replace it with gene A and Crispr package X"

Of course, it turns out any layman speculation I might have is out-of-date, witness this 2015 piece.