Bob, nothing wrong with the switch idea. I know of one case where someone had an Auber probe go bad (the drop-in type), and had to reconnect his stock controller to cook. But, I think that failure is not likely with the wall probe. The drop-in probe can fail for a couple of reasons: First, getting water inside it when cleaning, and secondly, letting it get too close to the smoke box in use. Both of those points of failure are eliminated with the permanent probe.
Never hurts to have a backup, but I haven't had a single problem with the bypass/permanent probe setup, and my smoker is used a lot.