If I manually turn off a D2MSD Decora Smart® Wi-Fi Motion Sensing Dimmer, should the lights turn back on with motion?

No. If a user manually turns off a D2MSD Decora Smart® Wi-Fi Motion Sensing Dimmer, the lights will stay off for 30 seconds.  The delay is built into the product to ensure you are able to exit the room when manually turning off the lights.  After 30 seconds, the motion detector will no longer be bypassed and will resume automatically controlling the lights.