Bookwyrm627: You only lose the gold in the bank if you visit Ravenshore after Blackwell Cooper is killed. I haven't checked what happens if you wipe out the Regnan fleet before going to Ravenshore; I suspect the bank sum gets zeroed as part of "lock every building in town", and thus the bank would be unaffected if you sink the fleet (therefore ending any pirate attack) after killing Cooper and before visiting Ravenshore again.
ZFR: Ah, so the vanishing gold is was not really a conscious decision made by the developers (which would have been a nice touch). When I first read it I thought it was, hence my post #3.
The vanishing gold could have been a conscious decision. I was simply speculating; I honestly don't know. Since gold in the bank is supposed to be safe, and all banks are connected, and considering the rushed nature of the game in a lot of areas, I'd assume "bug" rather than "feature".
Or the Regnans are just really, really good pirates, stealing money from the banks in Shadowspire and Balthazar's Lair from right under the noses of the Necromancers and Minotaurs. ;)
ZFR: Nice find. Do you get a message or dialogue about it in game, or do you just discover that your account is empty?
To answer this question: the money is just gone. In my test, I left a thousand gold in the bank to see what happens to it. It was simply gone after I visited Ravenshore during the pirate attack. Clearing out the Ravenshore pirates didn't help, and sinking the Regnan fleet after the money was gone didn't bring it back. It was gone from the Shadowspire bank as well (this was the only bank outside Ravenshore I bothered to check. I assume every other bank reacts the same as the Shadowspire bank).