For practical purposes---it is part of the screen unlike earlier models. As of July 2017 the price of replacement LCDs are far cheaper than trying to McGuyver a screen to replace just the home button flex.
"You can actually replace the home button extension cable but you'll need to desolder the backlight film from your lcd because if you don't , you'll lose fingerprint id . If you don't care for fingerprint, just replace the whole 3D touch + backlight film + home button assembly. This sits behind your lcd and is solderd to your lcd . You will desolder and re solder the new backlight into your lcd with the contacts underneath the backside of the lcd cable underneath black tape.
ALIEXPRESS SELLS THE IPHONE 7 3D TOUCH + HOME BUTTON Assembly for about $80. The whole screen will cost $350 +. So if your good with a soldering iron, you can save money.
""LCD Screen Display 3D Touch Film Module Part Flex Cable Ribbon Backlight Film Back Light Replacement For iPhone 7 / 7 plus 4.7""""
I ripped this cable when disassembling, but worked after soldering new 3d touch assembly in."
