In my setting, characters are (mostly mildly) superhuman in various ways. One aspect of this is that, as long as they're alive, The entirety of their body from the neck up (flesh, bones muscle, teeth, brain and all) is completely indestructible, as is their entire spinal column and all tissue immediately connected to it. The hands (up to and including the wrists) and feet (up to and including the ankles) are also indestructible just like the head and neck (I don't expect this to be important to the question but I thought I'd say so anyway just in case).
The rest of the body is also more durable than that of a real-life human, but I'd like to ignore that for the time being and focus specifically on the effects of these parts of the body becoming indestructible, and how it relates to a specific method of trauma that's going to be happening a lot in my story: fall damage.
What with the head being the most vulnerable part of the body when it comes to blunt force trauma, I imagine making this part of the body completely invincible will radically alter what it would take for someone to die of falling from a great height, as well as what injuries they would succumb to, and how quickly. And since one of the main obstacles the heroes are going to have to deal with is a suburb where humans are subjected to sideways gravity, getting a better idea of what heights these people would have to fall from in order to take lethal damage, and what that lethal damage would look like, is going to be pretty important.
If the head, neck and spine are completely indestructible, what's the next part of the body most vulnerable to lethal damage from a fall, and what kind of a fall would it take to inflict it?