Provided the probe is using a reasonable quality switch, switches are generally fairly repeatable.
Plus for woodworking, you generally don't need that high an accuracy.

I'll admit I personally use a mechanical tool setter on my mill, despite having a circuit board made up for adding a tool length sensor, but it does have a toolchanger, so I only have to set tools when changing them in holders.

I probably wouldn't get too hung up on emergency back up switches. Just make sure you have a screen that shows when the switch is actuated, and give it a quick press manually to check it's working before running the automatic tool setting routine.
Sometimes you can overthink things (I know I can be bad for it!), but simple is more often than not more than adequate.