I have been working on an app using Xamarin with Link-os plugin and ZQ510 printer. The idea of the app is that it can work in remote places where there is no internet connectivity.
The debug printing process always works. The iPhone can print without any problem with the Wi-Fi off and the data access off.
When the iPhone is disconnected from the PC and has some kind of data access, it is capable of printing. You can even remove the SIM card and connect it to a Wi-Fi without internet access and it will be able to print.