Really? You think just because half of humanity dies then the priceof Gold will drop?
Well...it never did in the past. I mean, when 50% of humanity died during the Bubonic plague, and 50% of those who survived went mad, Gold was still money. When people went into self-imposed isolation for years - as did the survivirs of the 14th century plagues - Gold was still money and held it's value.
When governments fell and madmen swarmed the streets - gold was still money and held it's value.
today's infrastructure would not do well if 3 billion people died. there would be such a surplus of goods that gold would not matter and the system would reset to bartering standards, mostly revolving around food.