Greetings!
This is Tin, I'll do my best to help.
Yes, you can format or reinstall your Windows OS to your PC even if your Internet cable is broken. The best option is just to perform a "Reset this PC", it's the built in feature of Windows. This is a good option as long as your recovery partition is intact. To do that, please click Start menu and type Reset this PC and hit enter. You will have 2 options there, you can use the keep files or remove everything. This process will reinstall the Windows on your device.
Thanks,
Tin