This is not econometrics though. Actual econometrics is upfront that you have missing data, performs partial identification rather than pretending that you have

This is not econometrics though. Actual econometrics is upfront that you have missing data, performs partial identification rather than pretending that you have point identification, and gives you upper and lower bounds on what the true parameter value might be. Only if you did that with this paper, you’d have bounds so wide that no useful conclusion could be drawn, as indicated by the author’s statement that without imputation such data is useless.