I don't know about the roaming, but with a duplicate sim, the data is currently pulled from your hotspot allotment, not the regular unlimited data.
At this time, you will most likely want to take your iPhone or put your original SIM card in the S7 if are going to travel internationally. Duplicate SIM cards and virtual numbers do not work internationally.
However, the DIGITS app will work internationally, so you could download it to your S7 and use calls and text that way. You wouldn't be able to simply take the S7 with the duplicate SIM as is and use it. Since the duplicate SIM card will not work internationally, data on the cellular network won't be an option. As such, the DIGITS app would have to work through WiFi if the duplicate SIM is in the device while roaming internationally.
I hope that helps!
OK, thanks for the clarification. Much appreciated.