When someone loses their head, their headgear completely disappears. This often makes me frustrated as raiders with good helmets just lose them when I accidently decapitate them. I'm not sure whether it was done on purpose or not, but I think it would be better if the hat was dropped next to the body.
If someone loses his head, i would assume, that the headgear get destroyed. Perhaps powerarmour could be there, or if a swort cut it clean off.
But if a weapon destroys the head (like a sniper rifle), mostly the headgear should be destroyed with it, i think.
Perhaps a random chance?
It depends on how it's destroyed.
In game terms, the head disappears, but that's an injury classification. It doesn't mean their head literally vanished into thin air.
Clothing and apparel are different.
It's working as intended. We assume that in all such cases the headgear is also destroyed. Thanks for reporting anyway.