and mostly on how much trouble and expense you can tolerate as opposed to the risk of failure. You could, of course, consider the failure modes and consequent effects of a CPLD failure. In some cases, a bigger CPLD with redundant circuitry within, and circuitry to monitor those, could work. You're still exposed, in that case, to a single-point failure. If you use separate devices, and redundant monitoring logic, you're still exposed, but considerably less.

RE