The NYAG say Bitfinex believes the cash was stolen. Bitfinex in their statement say "we have been informed that these Crypto Capital amounts are not lost but have been, in fact, seized and safeguarded". These two statements conflict with one another.
$370M of the missing money has been frozen by Polish authorities last year, due to someone using either Bitfinex or Crypto Capital to launder drug money. So technically that part of the money hasn't been 'lost', but seeing how long and drawn-out legal cases can become, years can pass before the funds will be returned.
I found
two articles to be about what I presume you are referring to.
Bitfinex had to borrow $700M from tether, out of the $850M that is unaccounted for. It would not be unreasonable to say Bitfinex had $150M in reserves.
If the $370M is in fact part of the $850M, Bitfinex's ability to recover the money will depend largely on if they were properly served with the seizure notice, and what they did to that customer's account.
Worse case scenario, if Bitfinex was properly served, but they eventually successfully processed a withdrawal for the customer despite the seizure notice, they will be on the hook for the entire $370M, and this money is in fact gone. If the customer for example withdrew bitcoin, deposited the bitcoin to binance for example, and binance properly froze access to the money, Bitfinex *might* be able to get the $370M back, but I am not an expert in this area, and am not explicitly sure.
A best case scenario is Bitfinex froze this customer's account and the account is currently containing at least $370M. In this case, Bitfinex could simply administratively debit the customer's account to cover the difference, and the customer could try to recover the money from Poland themselves if they have a legitimate claim to it.
If Bitfinex was not properly served with a seizure notice, and let the customer withdraw, the case becomes more complicated, and potentially will be drawn out.