There are so many versions of BIOS.
It sounds like you want to shutdown from the Fedora USB boot, then when the system is restarted it autoboots into Windows by default.
Typically a BIOS has a list of bootable types, and you can enable them, and reorder them.
If windows HD is first, and the F12 menu times out, then windows should boot.
If fedora USB is second, and the F12 menu times out, then windows should still boot.
If you hit F12 and navigate to the USB boot, you should get Fedora.
If this isn't how the BIOS is currently configured you will have to change the order.
If the hard drive fails, it's off to divorce court!