It 'may' go back. It really depends on how long ago you upgraded to 10. If by some chance it won't let you, which does happen when you have installed 10, then you would not be able to do it just from your computer's backup alone.
You can, however, get the original OS on CD/DVD or even on a USB and install it from there. I would check the manufacturer's website first to see if they have a free version for your device. Some do. Otherwise they may have one you can get pretty cheap.