The answer is to wire all your switches up in series to one pin. Go from the pin to one switch (normally closed contacts) to the next switch and so on, and the last switch is connected either to your 0v connection or your 5 volt connection, depending on what your breakout board requires.
On the Config/Ports and Pins/Inputs all the x y and z limts and homes are shown on the same pin. These are set up so that the normallly connected switches normally hold the limits and homes OFF. i.e. on my machine I connect directly to the computer so my switches are connected to 0v and NOT active high on the ports and pins. The internal pull up resistor is overcome by the switches and the leds are normally off. When activated, the line is no longer connected to 0v and the internal resistor pulls the pin up and switches it on.
As soon as any switch is activated, this breaks the connection and all pins show high - or activated. This doesn't matter - with a limit switch it is obvious which switch is activated from the position of the table, with a home switch, Mach is looking for the appropriate home switch anyway, and only reacts to that.
This has the added advantage, in that, if a wire comes off, or, as you say a switch becomes faulty, then it immediately trips the limits and your table will stop. You can find out which one it is by shorting them out in turn until you find the one that is activated.
As you probably know the state of all the input leds are shown on the diagnostics page
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