1. First, this is a non issue. Get divinity from GoG.
2. Second, nothing is eternal. I do not have the CDs from the games from 20 years ago anymore, in the same way I expect I won't have the games I have on steam right now anymore in another 20 years. Where's Steam shutting down any different from what we experienced with the 3,5" disks?
Even if I still *had* a floppy, I would not have my Amiga anymore, this is not even talking about the tapes for the VC20 (the computer before the C64 or stuff that ran on my 80286 (the younger ones of you probably do not even know what that means; you're probably running a 80986 with 64 bit extensions (with fancy market names as "Core" or "Phenom" instead of generation numbering)). Steam is nothing different, but the chances are much higher Steam will still be there in 20 years than the ones have been for 3,5" disks surviving. There's one reason where Steam sucks: when you have an unreliable net connection.
Btw, the executables from today's software *also* won't work on the PC hardware/operating systems in 20 years anyway, DRM or no DRM, net required or offline. So what's the big issue?
But go for 1. and stop worrying?
