There's tension between your request for a pack that "will last a very long time", and the "long-distance hiking" forum that your question is in. In general, long distance hikers look to keep pack weight down; certainly not all are gonzo ultra-lighters, but you don't tend to see many of the several-pound packs that are both more durable and feature-rich.

For me the right balance for really long-distance hiking is a ULA pack. My current pack has somewhere between 3000 and 4000 miles on it now, and it's still holding up pretty well. It's not as light as what some long-distance hikers use, but beyond durability it also has --- for me at least --- just the right limited set of 'features'.

So have a look at ULA packs. The sweet spot for me personally is their Circuit model; one hiking partner of mine did a lot of miles with their Catalyst (and liked it) but then switched to a Circuit. Hmm, the Ohm models look pretty good now that I look at the more recent options ... :-)