If that’s true and they do intend on shredding their copy on sale, what stops GitHub from buying it back themselves? (through a proxy, obv)
Therefore one way to weaken these criminals would be to weaken this trust factor. In a way therefore comments like "can we actually believe they will really shred it" goes towards this aim.
I have to wonder what criminal hacking gangs that do not operate on trust would do. Would it be like the replacement of organized crime (mafia) with the arguably wider damaging unorganized violent drug gangs?
More than likely they will just claim that the company paid the ransom and never release the code (or at least not immediately).