If I have read your post correctly
The NC PNP inductive proximity switches will of
pulled the Mk3/4 Planet CNC controller limit inputs up to +12V
destroying the inputs
The only solutions I can see is either
use the inputs IN1 to IN4 if the PlanetCNC software will let you
or replace the MK3/4 control board
Contact Planet CNC to see if they either repair the boards or offer a discount on a replacement
John