Some good comments above.
I guess the most important point from my perspective is that you either want "bombproof" gear or you want "ultralight" gear... the two are more or less mutually exclusive. Some ultralight stuff can be plenty durable, but it depends on how you use it. When I hear someone say they want gear that'll last a lifetime, those tend to be the people who use gear kind of hard. Of people I've met, they tend to be the ones who want gear they can toss in the back of the truck with the firewood and chains and not worry about the gear, you know? If it's something that you'll treat with care and respect each time you use it, any gear will last immeasurably longer.
If you want heirloom gear, you don't want gossamer fabrics. You want canvas and wool. Something like Filson. But then instead of a rain jacket, for example, that weighs 5 ounces you'll be talking about a rain jacket that weighs around 3 pounds.
I don't have nearly as much experience with cuben as others on this site yet, but the limited experiences I've had are that the "heavier" laminates are plenty durable. I'd be surprised if they aren't actually more durable than silnylon, but I guess that all depends on your reference points.