gpart destroy, in depth

Please: what, exactly, occurs when a partition table is destroyed by 
gpart(8)?

Background: a customer was 100% certain that no data was required from a 
hard disk in an iMac that will be disposed of. I booted from a USB drive 
with FreeBSD 14.0-CURRENT, then lazily ran gpart destroy for the 
internal disk (probably ada0). A few hours later, the customer realised 
that the disk probably held a few years' worth of important emails.

I don't intend to attempt recovery, or recreation of the partition 
table, but I'd like to provide enough technical information for a third 
party to advise the customer whether doing so will be economically viable.

(I see files such as lib/geom/part/geom_part.c and 
sys/geom/part/g_part.c, but I have no idea how to interpret them.)

Thanks

<https://github.com/freebsd/freebsd-src/blob/main/lib/geom/part/geom_part.c>

<https://github.com/freebsd/freebsd-src/blob/main/sys/geom/part/g_part.c>