[petsfed]

It is very tempting (and very easy) to think about firmware as simply software that you can update willy-nilly and at will, and things will always go back when things go bad. But there is a reason that most embedded firmware engineers are on their org's hardware team, and not software team. If I push a change that requires a JTAG to reverse, then from the customer's point of view, it is damaged.

The bootloader that allows you to revert back to prior firmware, is itself firmware. If that gets broken by a firmware update, then your device is effectively damaged.