Physical copies are far from the be-all, end-all of game preservation, especially these days. What you really want is DRM-free. Or, failing that, easily broken DRM, which is where Borderlands lies. BL4 will launch with Denuvo, but like everyone else, it will be phased out after the release period, because Denuvo charges per month, and then it's as preservable as any other game that can be played offline. What happens if the file gets corrupted? I use a copy that wasn't. What if the drive it's on dies? I use another copy. I'm not sure why you think these are gotcha questions or something.

Helldivers II literally withholds the server from you that prevents it from being playable in the future, and we've got a graveyard full of games built the same way that are all gone. But if a game is playable offline, it can be copied ad infinitum. If it's got LAN, its multiplayer can be played forever. I would spend $40 on Helldivers II if I enjoyed the concept of setting my money on fire, because it's built with an expiration date that doesn't need to be there. If I was looking for that in the same genre as Borderlands, I'd be playing Destiny 2.

There have been many games delisted over the years. That doesn't mean they are deleted from your account. Prime example is Prey (2006): it had a lot of music in it they had to license from large publishers and when that license expired, they no longer could sell it. They then delisted it in 2009. You can still get the code for Steam on places like eBay, activate it, and download it. It's very very rare that a game is both delisted and purged from CDNs. And in those cases it's because of malware or other suspicious activity (like undisclosed crypto mining, etc IIRC).

I'd do the same thing if the disc scratches. I'd download a cracked version from a weird Polish website.