The rules are simply not set up well to allow fleeing. You start engaged, eat an attack of opportunity, then end up engaged after they catch up. Any slower companions (small or heavy armor wearers) are left behind to die. The chase rules are also awful. 5E (and D&D in general) is simply not set up mechanically well to allow for players to escape without magic or the DM just letting you get away.I think this "death spiral" malarky is just a screen to say "I don't want things to change" or "I like the system the way it is" or "Wounds are fine and 5e is the best thing since sliced bread."
The only way you end up in a death spiral is if you continue to press on when you get injured, or your ability to do what you do. And you know what you do then, you flee. You leave the fight. Not every fight needs to be to the death. You take a week to recover. Gee, I'm at 2 Exhaustion, let's keep going deeper into the dungeon! Let's go fight the BBG. No, how about you wait and recover first. And if its impossible to flee or have the time to rest (due to the way ticking clocks and "adventure paths" work now), that's a table issue, not a game issue. We play older school rules with much lower hit points, non-balanced encounters, etc. and both monsters and characters flee fights they can't win. If I'm poisoned, I'm not going anywhere. If I'm non combat capable in a fight, we're withdrawing, and the game/table accommodates that.
I like @Steampunkette's suggestion about a critical doing 1 vitality. 5e is simple at its core, it needs more dials to turn, especially around healing. Their gritty healing seems half baked.