Nobody working at ND really is a the lower end of any food chain. They all have enough oportunities beside staying there, as proven empirically by the fact that many DID leave to go work somewhere else. If ND's work/life balance is unsustainable, that will manifest in their products, and the company will wither on their own. And I think this process is much more accelerated the more the employees embrace a personal culture of responsability than by external intervention. Employees voting with their feet so to speak, by settling at the places that actually deserve their talents, has a way more powerful transformational power than theoretical laws and regulations ever can. That's all in my opinion of course.
How many left voluntarily? Temporary contracts are a thing in game development. There is nothing to say that all those that left ND, left on their own accord and onto better pastures.
Treatment of contractors is another dirty side of development.