I strongly concur with the idea of systemic redundancy. In the case of E911 location systems, for example, some of them are programmed with the notion of fallbacks, such that the appropriate Public Safety folks get a reasonably precise location where it is available, and a less precise one (along with information about its precision) when the most precise location is not available, continuing to fall back to less and less precise information.

In general, if my life were at stake, I would prefer that your system be cross-checked by a robust set of independent production processes (and human agents) to maximize my chances (in addition to an exhaustive test suite).