After dead-zones carrier is dropped until restart So I'm assuming this has to be a property that can be changed through buildprop, but I thought I'd consult you guys first.

Phone: Unlocked Galaxy S7 (Sprint), Android 6.0.1

Network: T-Mobile

Issue: If disconnected from the GSM network(in a deadzone/tunnel/big building), the device will continue to stay disconnected until it has been powered off or restarted, even if its in an area with known coverage. 

I checked the APN while it was "disconnected" and it still detects a SIM is installed and all the carrier settings are good, but it wont reconnect to the carrier unless it is restarted.
Solved it myself after tinkering with it for the last day. While not recommended, it is possible to flash the Galaxy with other carrier's "version" of the android OS. So the old stock Sprint operating system was removed and replaced with a T-Mobile variant which changes all of the settings to GSM on the back-end for me. If you move from carrier to carrier and experience no issues... I highly recommend the "ain't broke, don't fix it route."


First by putting the phone into download mode (home+pwr+volume down)
Connecting the device to the computer, and running ODIN
Installing a T-Mobile variant of the S7 ROM (this will essentially change it from a 930S to 930T)


Downloads included:


New OS, I used "G930TTMB3APG1", but your mileage may vary depending on what carrier you need to change to. 
ODIN 3.12.3