Q: Is the MAX7357 high impedance on the SDx and SCx lines when there is no power applied?
A: Yes. Tests show that with the IC's GND connected and VCC floating, a 5V DC source connected to the SDx and SCx pins does not register any current on a handheld DMM with 10uA sensitivity. This indicates that the input impedance of the pins with the device powered off is greater than 500kOhm.