Actually yes, this happened twice this year at my bank, operation were halted for 48 hours the first time and 6 hours the second time. The whole bloody bank stopped working for 2 days while IT people were scrambling to find and correct the problem. And still the bank retained the userbase bevause peopel are lazy and the bank compensates people who can substantiate claims that they had losses (because they couldn't buy or sell a financial instrument or repay a debt that was due, etc.)