Well you could have it so that an attack module would attack a bank. Most RPGs I’ve played though have had it so that the bank is a protected asset, one that can’t be stolen. I would recommend looking into the design of your RPG to include some of the Ideas below:
-implement upgradeable skill sets where after certain level achieved, a skill set can be purchased. One of which allows you to rob a players bank.
-implement quests where you rob a central bank, and if succeed you steal a portion of x number of players who have deposited money in the bank.
-implement a city/world system where people are located in the same city/town and have a central bank system.
-implement a army/castle system where you employ and train soldiers or crooks to sneak in and rob resources of a player.
Many ideas but modules would have to be built for it all.