Software doesn't have to last 50 years, but if you want it to, first build hardware that'll last 50 years, and make it upgradeable. Otherwise you'll be trying to get an emulator to work to fake out the software to think it's still running the same platform. And that's to say nothing of networking and application standards changing, or, say, a lack of mirrors, and tons of runtime dependencies.

Linux-packaged software will survive, because it's based on a system of lots of mirrors. But most new software isn't packaged, it's just available as source modules on one or two sites, or in GitHub releases. Who's mirroring all that?