"When these two bodies finally merge, the black hole will typically swallow the neutron star whole."
Not whole.
A small amount of matter will escape, both iron nuclei (from the crust) and free neutrons.
The R-process of stellar nucleosynthesis will then take place.
As I understand it, a normal output between three and 13 earth masses of gold is typical.
This total mass is insignificant compared to the final mass of the combined object, but it is also the engine that creates many elements higher than iron on the periodic table.