I have also reused sensors without any problems. But you have to change the pads right when the check brake lining light come on. Because if you don't and keep driving, then the sensor will wear and you cannot reuse them.

But for practical purposes, I now change them when doing the brakes because if it is worn and I have to take them apart again, I get pissed off at myself trying to save $30 and my time is worth more than that. So just change them and not think about it.