What you need to preserve it are games sold on GOG and other DRM-free stores.
Nah, you need pirates. You need something like what what.cd was, an archive built by enthusiasts driven by quality and the desire to have untampered original copies. (Plus patches & cracks when needed). You need abandonware sites. GOG and other DRM-free stores are subject to the whims of publishers & developers and random rightsholders. They are not in the business of archiving games. They will host censored versions…
As for preserving in other ways - I agree, you can't expect any specific store to be around in the future.
Internet Archive also work on preserving old games.