Are there usually consequences for attempted duplicate publication?
Good question. First of all, as far as I know, there is no penal system in academic publishing. Reputation is everything. (BTW Many of us have made big or small mistakes when we were young and ignorant, learned our lesson, everyone moved on.) Of course, a journal could always shun authors "indefinitely", if they attempt to violate codes of conduct. There is not much more a single publisher can do. In cases like yours, the responsibility falls back entirely on the academic community - whose members are also editors and referees like you - and the control power of one's reputation within it. 

In your particular case, as you said, the editor presumably consulted with the editor-in-chief, which shows it is not a trivial problem to handle, and they decided to proceed as they did. If the journal had rules in place, such as that they would have to refuse future submissions from the same authors, they would inform the authors, but that's obviously not the case. 

You did not specify if those authors are known in your field or obscure. If the editor knows the author personally (which I doubt in your case), the dynamics is different.