That key will never be used.

Not only is their no financial incentive like you said, but there is a very fucking huge juridical disincentive to needlessly associate oneself with one's past crimes. Which I would assume holds doubly true for 'kingpin' statute violations and laws covering conspiracy to commit and engage in international narcotics trafficking.

The only way I could see your eponymous benefactors signing anything with that 2020 key is if they opened another market on the DL and ran it until it regained its former position/prestige. Then, after enough months had passed that it'd be a given- that should the owners be caught - they would be facing life in prison - then and only then could I picture them taking off the mask and admitting:

BTW, we're Agora :-)

But still, even that would be seen as pretty reckless. It's just not their style. If they were going to visibly come back (i.e. use the updated key) - it would have been within a month or so of them pausing operations, imho.