2 things. one, if there is a second line, that should not affect the sensor line logic.

two, I was wondering if short to ground is a failure mode for temp sensors in gneral.
That is I understand open, IE no resistance at all, but what if it shorts to ground instead?
or is that a high resistance reading?

you would have to put in a jumper for the sensor line if you used the ground line instead. so maybe no better than just a switch for the single sensor line to switch from reading ground to resistance.