I have no experience of blades causing damage to tube bundles but I would not rule it out if your ACC is an induced draft W style. Potential damage to the ACC structure should not be a concern. The Oh Shit! vibration trip switch should safely shutdown the motor within a few seconds of the fan blade detachment. Unlike most rotating equipment e.g. pumps and turbines the protective vibration sensors or switches typically aren’t preemptive but more so installed to shutdown upon or ater fan blade failure.