Chosen Solution

So the cable snapped off when I tried to disconnect the display. Does this mean this phone will never get get FaceID working again?

I obviously have the original sensors, but I guess it’s not possible to replace just the flex cable?

It depends on if the cable is plug in type or soldered in. You can replace it if the part is available yet.

Actually you can transplant these sensors onto a new flex cable. As described in the repair guide. ‘Prepare a new flex cable. Apply some Paste Flux to the bonding pad and solder the detached Flood illuminator module. ‘ How to Fix iPhone X Face ID Not Working After Screen Replacement