CoPilot's map data is held locally on the device, so as long as CoPilot can still obtain a GPS fix, it will continue to navigate the planned route. If mobile network coverage is lost for an extended period of time live services such as ActiveTraffic may not be available, but navigation will continue. 

In instances when GPS signal is also lost, such as passing through a tunnel, CoPilot will extrapolate the route until a GPS fix is returned.