When someone deposits at a bank, they don't accept to take any risk as to if the bank will or will not make good investments. If the bank cannot pay depositors, it has to default.
That's correct. But that's because a case where the losses are equally the fault of the bank and those who loaned the bank money are rare. However, if you imagine such a case, it should seem clear they should split the losses.
As a silly example, suppose I tell you that I feel really lucky on the slots today and that if you give me $50, I believe I'll win $100 and split the profits with you. Say you also believe that this is the case and therefore loan me the money, fully believing that I will win $100 and split the profits with you. In this case, if I lose the $50, it's not fair for me to be responsible to you for the entire $50, lost profits, and so on. When you have a common mistake, made equally by both parties, with no significantly greater fault falling on either party, it is inequitable to try to enforce the contract as agreed. In our gambling case, our contract never addresses the case where I lose money because neither of us considered it possible -- it can't say what should happen in that case because neither of us ever tried to make it do so.
However, in this case, the issue is not the default or partial payment. It's that Patrick Harnett chose to operate as himself, and he took deposits in his name and should not default on deposits if he does not default himself as an individual and keeping his personal wealth. The risks of operating under your own name instead of managing a legally separate entity.
The issue in this case is that both Patrick and those who loaned him money made precisely the same mistake, and neither party would have entered into the agreement but for that mistake.