This happens fairly frequently - maybe 40% of the time during my testing. The termination code is 11. Basically, the stdout indicates that ios-deploy is waiting for a device to be connected (I have a 10s timeout), and then immediately terminates with a code 11 - without trying to install the app.
Sometimes the error will occur repeatedly as I re-run ios-deploy. Sometimes it seems to go away by itself. Sometimes it goes away after I disconnect and reconnect the device.