You'll just get less capacity if BMS was wired to monitor individual cells and reported capacity based on that. If you were just measuring voltages at the bus bar, you could over-drain or otherwise over-strain the outlier cell and set it on fire.

Which don't happen often enough to make Amazon do something about fake packs for drills and Dyson vacuums, but I think the chance increases as cell count increases and idiot-proofness decreases.