@loosus456 Without directly knowing your setup I might be a little off the track with my guesses but here it goes, see what itās worth for:
You need some kind of EFI boot manager (entry) to boot Windows. This is what Boot Camp usually does for you and it can be done using rEFInd for example as well. This boot entry is partly stored in NVRAM (not on disk) an therefore will persist even if you delete the macOS partition. But that doesnāt mean that you donāt need that. I think there is a chance you can do what you want because FOG comes with rEFInd on board that can start Windows straight from PXE booting. PXE to the FOG menu and default exit style rEFInd should do the trick. That gets me to your second question.
You can use USB keys to boot up into the FOG menu - this is not essentially PXE booted but itās still partly network booting after the initial boot from USB. But you can also fully PXE most Macs! Take a look at our wiki article on this. One simple method I like is blessing the Mac so it does load iPXE straight from the FOG TFTP server without you having to setup DHCP properly. But in your case I donāt think thatās a good option because once macOS is gone itāll be very hard to change the blessing later on. So you can either go the āUsing stonesā¦ā method or set the Macs to netboot before deleting macOS - the later has a similar issue to the āUsing stonesā method because you canāt easily change the bootup setting if macOS is not installed anymore.
I donāt know of any tool that can set boot configuration in NVRAM on Macs other than macOS itself. Possibly tools exist but I donāt know of any. Maybe it can be done using a macOS boot USB key? Give it a go and let us know!
Special note: There is one particular ethernet card in some Macs that do have an issue with iPXE on macOS Sierra and newer - see here! I am working on this but I canāt say when Iāll get that fixed. But itās only that one particular NIC as far as we know - Broadcom 57765. Take a look at the device manager (About my Mac) to see if you have that NIC in your Macs.