So, lets imagine you have been running this continuously from the beginning and there is absolutely nothing fishy on the chain of the events of the ledger that makes this proof. All customer deposits (1B worth of coins) are backed by respective assets (1B) in the portfolio. Unfortunately the business has been run badly, and in addition to this portfolio, the exchange has assets of one worthless laptop, but there are some tax liabilities worth 2B and an just found loan payable to Italian Mafia worth also 2B. Tax authorities file for bankruptcy.

1. How does the exchange ensure money is paid to the customers instead of Mafia or tax authorities?

2. If/when it can't, how these liabilities are included in the proof of liabilities?

(note: this is a real and difficult problem. That's why there are laws, regulations and deposit insurances around customer funds in finance, which, yes, fail occasionally. I just do not see how that can be solved by blockchain.)