Prior thread. You are not required to close the account, hence, there is no fine for failing to do so. The regulators do not give even broad direction regarding account closure, but individual examiners oftentimes have no qualms about telling the bank what it should have done.
If you are certain they are
only structuring, they are still imposing a significant burden on your bank; i.e. at some point it's a cost issue, not a legal issue as to whether you continue to monitor, research and file SAR after SAR.