> if the thief could use an AFU exploit to tell the SE to only trigger the reboot after 300 days, the entire feature becomes useless

Then why not simply hardcode some fixed modes of operation? Just as an example, a forced choice between 12, 24, 48, or a maximum of 72 hours. You can't cheat your way into convincing the SE to set an unlimited reset timer. I'm sure there must be a better reason.