If you don't have a Windows machine, it'd be good if we knew what you do have in order to guide you properly.
Flashing back to stock on Linux is quite easy once you've got the tools set up. I would assume MacOS X is similar provided you can get a suitable fastboot or mfastboot binary. (I recommend having them in a directeory listed in your $PATH variable with proper permissions for USB so that you don't need to sudo to use them.)
If you've got no computer, but can boot in a modified recovery, it should be possible to flash the entire stock ROM with that. You wouldn't be able to relock the bootloader though, if that's something you were aiming for.
My phones: Galaxy Note II SGH-T889V (with LTE enabled
/ ext4 SD card support on TouchWiz ROMs
), Motorola XT-1045 Moto G LTE (TWRP
Previous phones: Nexus S GT-I9020A, Galaxy Gio GT-S5660M (Arpeggiomod ROM
/ Discussion, stock rooted ROM
), Motorola XT-1032 Moto G.
Phones for which I play "tech support" for family and friends: Galaxy Nexus GT-I9250, Galaxy Q SGH-T589R, Galaxy 551 GT-I5510M, LG C-800G Eclypse, Motorola XT-1032 Moto G