Bede,
I'm not so sure about this one. i did read comment #23 left on Mike's blog. Some of the information may remain on some of the directories but not all the directories. I know for sure Yelp will revert back as do others.
Why be enslaved to Yext? As an agency I can't put all my eggs in one basket. I'd rather take the time and submit my clients information manually and be done with it. What happens when you do cancel a subscription with Yext? Are you going to spend the next several months continually checking 45 directories to see if the information has reverted back?
The only advantage Yext brings to the table is if you constantly run coupons and/or run daily, weekly or monthly specials. In this case the coupons and/or specials get updated across the board on many directories at the same time.
Yext is suited for single business owners who know little about citation building. If you are an agency you must build citations manually for your clients.
Just my two cents.