It is exactly the reason why they had to call in the liquidators - because they cannot use other peoples funds or continue trading if they are insolvent.
That's not true. You don't have to involve a liquidator if you want to close a business. You simply close it, pay back all the concerned parties and that's that. And make no mistake, this is a voluntary liquidation, no one forced it upon them. It clearly says so in their company filings. A question remains: if voluntary, why not first receivership but straight to liquidation? Contrasting this with all their tweets saying they are on the way to resuming normal activity?
It doesn't even necessarily mean that there is not enough funds to cover the debt. It could be that they do not have enough cash at hand to pay for their bills going forward.
Again, wrong. The only real reason why one would call a liquidator is because they can't pay back and seek the protection of the liquidation process. No one is crazy to call someone who gets a fat cut if they can simply close a company.
Of course it's not that simple, we don't know how much was hacked, if indeed was a hack. Again, no reason not to post the hack TX, unless you want to hide something: amount, destination etc. So complete secrecy about the hack + voluntary liquidation = draw your own conclusions.