[Kiwami]

As far as I remember, every single HumaGear (aside from a few selected ones, spoilers so I won’t go into detail) has a cloud backup, so when they are destroyed Hiden produces an identical copy and loads the backup into it.

Aruto's rage and sadness stems less from the fact that the ones he destroys don’t come back or only in an altered way, but from his personal views. He believes HumaGear to be individuals and part of his family, so the act of them getting hacked which forces him to attack and destroy them is what upsets him.

The daughter from episode 6 is an exception to the rule as her appearance was illegal, it is forbidden for HumaGear to bear the resemblance of deceased people who cannot consent to this act, and so after she was destroyed she couldn’t be replaced.

I was also confused by this early on because the act of replacement was never really shown until later and the backup was explained in a completely different context.