Proximity Switches

Hi all
I am starting to build a CNC plasma, I am going to control it with a Mesa 7i76e and use closed loop steppers.
I am planning on using PNP proximity switches for all axes's (home & limit). Which type of switch NC or NO would be better (safer) to use in the off chance that I lost power to one or had a wire break?
The CNC router I have previously built, I used NC rotating arm/plunger switches so if anything went wrong with the circuit it would bring up a fault and stop right away.
I am trying to make this machine as fail safe as possible. I don't have any prox switches to test so I am unsure what they will do with power loss or break.
All comments welcomed.

Regards
Philip

NC is always the safer system
it will tell you when it is broken and let the mashine not HOME
as the switch is closed it will RUN to the safe pos away from the switch
HERE You see the switches in action