Phlarp's original comment was about 'a "Range Safety Officer" on the ground whose entire job is to determine if and when to deploy this self destruct system.'
The text I quoted implies there is an onboard flight termination system, even if there is no Range Safety Officer who can send external commands.
FWIW, a part from an exploded rocket, like the engine, could still destroy a school bus filled with children. The odds are very hard to estimate, and made more complicated in that there are few failure modes where a rocket failure halfway across a continent, at supersonic speeds, would reach the ground without breaking long before.
An unpredictable, malfunctioning rocket could still million-to-one itself onto a school bus filled with children, halfway across a continent.