...Ridaya tilts her head at Sophie. "Like, a normal lightning bolt from a storm?"

"Approximately, yes."

Ridaya thinks for a bit. "...That could maybe kill an eighth circle wizard. If it was an unusually large lightning bolt. And they were asleep. And  really, really unlucky. And not especially tough. And had no relevant precautions. ...I would have to get decently unlucky for a single strike of lightning to kill me, and the rest of my family is more durable than I am, Zan significantly so..."

Hrm. She remembers how distressed the falling made Sophie. "...it's not like that, where you're from? People don't get harder to kill as they get more powerful?" 

Sophie's eyes widen. "No? Not really? I mean – there's Long, the ones who've gone further into the mysteries, done something to make themselves less human. They don't age, and some kinds of them can live through some really dire things. But... I'd have put the woman with the scarf in that category, if I'd been thinking. Not you or Luto. You know when you're dealing with Long."

"Huh. Here it's... more gradual than that, and less obvious. But even without the boots, Luto wouldn't have died from that fall. She'd've been hurt, for sure, but nothing she couldn't sleep off in a few days." 

"Well. Now I know not to worry too much for you, I suppose."

And to work on something that could kill Long. There are weapons beyond what she yet knows.

Ridaya nods. "Sorry we scared you about it! It honestly didn't occur to me, that it would be a way worlds might be different?"

Uma did a deep dive on this once, because she was tired of reading conflicting half-baked theories about why this happens (she'd never been a fan of the common magical healing makes people tougher over time), and... "Even on a plane that has no magic, people who fight and risk their lives get stronger and harder to kill in the way we're used to, so it seemed like a world with strange magic would work like that too..." 

"But wait," the careful reader may cry out, "Where would Umakhi have read about that? How would someone even know that? How do you even go to a plane with no magic?"

The answer to those questions, in reverse order, is:

a) Greater Create Demiplane can adjust an existing demiplane such that magic simply does not function at all there, with the sole exception of an already-extant permanent planar portal into and out of the space. The demiplane in question can even be permanent, if the caster is willing to spend the money on it.

b) An archmage in possession of the wealth and means to create such a demiplane, an interest in this non-trivial question about the reality they inhabit, and an utter lack of respect for the lives of ordinary people might kidnap some population, force them to live out a few generations in their null-magic demiplane, and then force some of them to fight for their lives repeatedly there and see whether they level normally. (And with Golarion being the type of place that it is, this has happened at least thrice over the ages.)

c) Some archmage who lived over a thousand years before the breaking did this to Win An Argument, and she offhandedly reported the results of this experiment as part of a massive set collection of work titled "Khier Chhiril¹ was a worthless fucking hack and you should go piss on his grave"², which Umakhi managed to find a copy of at some point and read cover-to-cover on one of the partycule's intercontinental boat rides.

1: Khier Chhiril, Umakhi can tell you, was a seventh circle cleric of Qi Zhong famous for his prolific (and mostly accurate) writings on the basic nature of reality, magic, life, and the planes; much of his work is well-respected even today. He died about five hundred years before the archmage in question published her work.

2: The collection did also contain some less esoteric corrections of Chhiril's work scattered in, but 90% of it is just an unorganized list of very specific and nasty tidbits about the man's personal life, all of them essentially unverifiable.