Black-market drug sales probably won't be too affected by the crash, they already had a network before Bitcoin.
But ransomware! Oh man, that's nowhere near as easy nor as profitable without a high-value cruptocurrency. If the crypto crash ALSO took out ransomware developers, that's two birds with one stone, as far as I'm concerned.
That'd be great, but so long as there is some nominal value in cash to some cryptocurrency, wouldn't ransomware just ask for the same amount of underlying money? That is, just increase the number of coins required for ransom? The big benefit in cryptocoins for ransomware isn't the increasing value, but the fact there is no intermediary that can turn off accounts or rollback transactions.
It's the same with the dark markets. It's not like dealers are suddenly going to charge less money for drugs now just because the intermediary transaction currency is worth less.
A low valuation might affect coinminer malware though.
Banks are much happier to deal with you when your source of income is "The Apple Store", instead of a crypto exchange.