ANYTHING "could" fail without warning.
But your thermostat DID NOT.
In fact, it didn't "fail" at all. Neither did it give no warning.
Instead, it warned you that it had a low battery. How long were you planning on going on vacation for? If it was only 2 weeks or so, it probably would have still been saying "low battery" when you got back.
Do you get this hysterical about everything?
BTW, I note that your original post said something like you "had to" go on vacation. Interesting passive aggressiv phrasing. Like to make sure everybody knows you did nothing voluntarily, so therefore nothing could possibly your "fault"?