Permadeath has always been intended to be a trait that's in by or before the beta. It will be something you opt into for additional trait points. The way it will work is that if you're downed, you get a permadeath warning and an effect on you to remind you that you're close to death. The effect will progress each time you're downed, and after the 4th time you get downed you'll drop everything on the floor and your character will be deleted (the body will linger for a little while).
In order to reset the effect you'll have to go for a certain amount of time without being downed, which increases with each stage of it. Then you'll have those strikes progressively stripped until you're back to normal.