How to deal with coauthors that have left academia Researchers might take different paths other than staying in academia after completing their PhD, postdoc or even later. This happens for a number of reasons. The most compelling of all is that there is not enough room for everyone, but it could happen that these people lose interest in research, find a good opportunity in the private sector, or (more often than we'd like) get burnt out.

For a typical researcher, there is a body of work that they have done and is susceptible to be published by people who they were collaborating with after they have left. However -beyond possible personal satisfaction- they do not have the motivation or time to publish this work anymore. This leads to poor communication between the authors that stay and the person that left, usually motivated by the latter not replying (perhaps reading) emails concerning the work or taking too long to do so. These people will usually be fine with having their names on a new publication even without the need to go through the manuscript before submission (this might also be true for reckless researchers in general, but that's another story...) because they might not be concerned about their (former) career in academia anymore.

How should this situation be dealt with? Is it ethical to submit a paper when a coauthor that left academia has not actively taken part in the preparation/proof reading of the manuscript, considering he/she has contributed significantly to the work?
First of all, it doesn't matter where, how, or even if a person is employed.  Science can be done by anyone, anywhere, "academia" or not. Assuming the person has made significant contribution by the standards of your field, the only things that matter are:


Is it possible to contact them?
Do they want to be an author?


If they have contributed significantly and want to be an author, it is dishonest to not list them as an author.  If they've dropped out of research entirely, you may find yourself doing the writing work without their help, but they still should be an author.  If you can't contact them, err on the side of inclusion.

In fact, this is a place where I disagree with the letter of the Vancouver Protocol, which states that somebody can only be an author if they are significantly involved with preparation of the manuscript.  The spirit of the Vancouver Protocol is to prevent "gift authorship" and other unethical types of inclusion.  Imagine, however, writing an acknowledgement that says: "John Smith did all of the experimental work, but the long hours burned him out, so he left for a job at Netflix and we cut him out of the author list."  To me, at least, this feels like denying credit inappropriately.