I don’t think that even technically it will be possible to put up such a volume for sale on official exchanges. Again - do not forget about regulatory risks, I'm sure exchanges have a set of rules that came from regulators on how to behave in some situations, including the release of significant volumes to the market, which can lead to pronounced negative consequences. Account blocking "for trial" - and the drain was stopped ..
Despite on having those strict regulation they could still able to pull it off even though not in bulks but it would be still significant.Every exchange hacks and the stolen coins
attached to it would surely be creating not only on mental but also in emotional aspect on which it could stir up the entire market on that case.
It's not just that I indicated the "mental abilities" of the thieves, in quotation marks I wonder what they hoped for when they planned an operation to turn such a huge amount into fiat money. It was an absolutely idiotic act that did not have a single logical explanation!