The nature of the Sundering has been spelled out in a Nier Reincarnation side story.

[Rulakir]

A couple days ago, a new event series focusing on Emet-Selch was released written by Natsuko Ishikawa.

This is confirmed? Faith restored in Ishikawa.

I hope this stuff will settle the "was the Sundering murder?" question in favor of "yeah", since it's clear it completely destroyed people's identities and even physical forms, but I kinda doubt it.

Not to mention: "In the simplest of ways, they die and die." Given they were devolved to such a primitive state it's likely their life expectancy was short as well, probably dying to things like the common cold and infections from cuts. What a horrific thought.