To be honest, with the Thor there's very little to go wrong. The entire light consists of the following:
Plastic case: Thick and tough plastic.
Biiiig reflector: Metal.
Lens: Thick glass. Probably the most fragile component.
Bulb: Seems to be pretty tough, but easily replaceable.
Switches: Seem to be well made, and again, are replaceable.
Battery: Be sensible with the charging times and don't deep discharge it and it'll serve you well.
Charger: In the case of the one I had, it's one of the most well built wall warts I've encountered.
Basically, so long as you're moderately sensible, it should serve you for years. The main problem with the Thor is its great weight. Drop it from any real height, and the weight will lead to it taking quite a beating on hitting the ground. Though I can't afford to test that theory! That and that the light isn't weatherproof. Thanks to the vented design, it would be hard to weatherproof it though. And it can survive a light shower anyway, that I've proved!
It's a tough light for the money it costs!