I have a pair of Ortlieb back rollers that I've had for several seasons. I've loaded them up pretty heavy loads: brick pavers, circular saw/percussion drill, truck brake rotors/drums (these suckers are heavy) and those small kegs you get from microbreweries (one in each pannier). The panniers haven't failed me yet and I don't think they will in the future.

I've seen quite a few older beat to all hell looking Ortliebs here in Deutschland that are still being used on their owners bikes. If you do break a piece on the pannier, parts are readily available.