This is one of the first things they test. Even if an app needs a network connection to work, the lack of it should never produce a crash.
Some thoughts (untested)
If you are using the Local Builder perhaps you could reproduce the problem in debug mode with an isolated local wifi (just LAN, no WAN) and no cellular data in your iPhone, or
if you are using the Hosted Builder, another possible approach would be to build the Release app and install it, then disconnect the router from the WAN, also the cellular data from your iphone, and send the logs through UDP to a local server.