In this scenario, the extortionist and the drug dealer are
the same party. The goal of the scam isn't extort $500k. That number is as real as my uncle's Nigerian inheritance. The goal is to extort the mark of $150k, and make him a) maximally disinclined to attempt to tell about the scam (by making him complicit in a "murder", much like 419 scammers generally try to make the marks complicit in defrauding Nigeria) and b) give the scammers the opportunity to come after him again, in the future. (One possible scenario: the "hitman" "hired" by the "drug dealer" for the "murder" attempts to shake down DPR in the future, threatening to expose his involvement in the murder unless he is paid off. The hitman is still the drug dealer is still the extortionist.)
The game theory of scam artists is really simple: your expected probability of scam N+1 working goes way the heck up if you've successfully worked that mark in scam N. That's why you can literally find people selling lists of folks who've fallen for 419 scams.