I think the average person would take a very dim view of Aegean cancelling the tickets. Most people assume that once you've paid the agent for the ticket the airline has been paid (a view that I also held!). Therefore, if Aegean were to cancel the tickets it would leave a very bitter aftertaste for most, especially after making all their summer holiday plans (i.e. hotel, travel arrangements, tickets for attractions). They might possibly focus more of their anger at the airline rather than the company that sold the tickets, and no longer exists anyway!
Of course we don't know that actual amount that A3 is likely to lose, but they have to consider the PR aspect in all this in their decision. As a rational person I would understand if they decided to cancel the tickets....but I hope they don't!
One thing I don't understand in all this is this, if an airline goes bust, it's quite common that the customer loses their money even if the tickets was booked through an agent. If it's the case that the airline hasn't been paid until after the flight anyway, why isn't the money simply returned to the customer? I know it's the case that you can often get your money back from the credit/debit card company or travel insurance, but it seems to me the travel agents/airlines work the system so that the customer always loses out.