I'm stunned. For a change, a Legends & Lore article that actually makes me more enthusiastic for the new edition. My hit points must be low - I failed to get an Extended Rest last night.
I quite like the idea put forward in the article. I'm not sure, though, whether it's better as "if the attack leaves you below X hit points, save or die" or if it's better as "if the attack does more than X damage, save or die". (Or, how about this - the spell causes a lesser effect normally, but if it scores a critical hit, it becomes save or die?)
I think perhaps it's also a mistake tying everything to hit points. It sounds to me like the game may well benefit from a "mental analogue" to hit points - another pool that is used to ward off domination, fear effects, insanity, and the like.