The key would seem to be if the part that fails is easily replaceable, then. If I make a design that has a part meant to fail-safe in a situation that would ot

The key would seem to be if the part that fails is easily replaceable, then. If I make a design that has a part meant to fail-safe in a situation that would otherwise be dangerous to the other devices (I'm an EE rather than an ME, so we'll call it a "fuse"), the good-faith repairability practice is to put the part in an accessible location and make it a part that is readily available. If I wanted to encourage replacement of the whole device, maybe I make it a soldered-on part in the potted section of the PCB.