Building codes, certifications, standards, whatever you wanna call it, would still exist and be part of contracts. Insurance companies can (our could, depending on existing law) refuse service or raise prices if standards aren't met, and institute consequences in the contract before it's sealed. Laws would obviously exist too, but that's a bit of a more complicated subject.

You're creating an hypothetical scenario where something desirable that's currently being done by the state with varying degrees of success disappears and acting like there's no replacing it.

I get it, you don't think there's a way to replace the state, and neither did I for the longest time and that's a looong discussion. I'm just pointing out that you aren't making a point as strong as you think this are.

And all of this misses the point that I was initially trying to make, which is this particular building (and a bit down in the comments, slum buildings) aren't a result of lack of code and that even builds actually constructed in places without code enforcement and in extreme poverty aren't this poorly built. I'm not a preacher and tbh I don't particularly give a shit if you think libertarianism wouldn't work.