In the article the authors discuss that over the course of the study a few of the participants who were in the vaping group stopped all together, and also a few of the control began smoking (vaping). So I believe they would actually have this data, though they did not discuss it in detail. Perhaps because it did not show a difference since there weren't any differences between the test and control groups anyway.

Now things clearly would be different were the authors sampling traditional cigarette smokers.