Question: The MAX14756 is listed as normally closed (NC). If the device is unpowered, will it pass signals and have its closed on-resistance through the A_ to B_ paths?
Answer: No, the NC designation just refers to how the device responds to control signals when powered. If the device is unpowered, it would not operate normally with a low on-resistance path between A_ and B_. If signals are present at the A_ and B_ terminals while the device is not powered (VDD = 0V), ensure that the absolute maximum ratings are not exceeded (datasheet, page 2):
A_, B_ to VSS............................... -0.3V to (VDD + 2V) or 100mA (whichever occurs first)