This is a very persistent rumor. I forget the details but it comes from a customer support email, not some official statement or promise from Gabe, and even that was originally posted on a long gone forum which you can only find quotes of. Even if there was first hand proof of an official statement, I wouldn't expect it to be upheld. Minecraft's website used to have a line from Notch saying he would make it open-source in the future.
Steam DRM is and has been for decades famously easy to crack. Literally look up steam auto cracker and crack all your games in couple minutes. It is also optional by the way. I much rather have weak but popular steam DRM that makes it less likely devs use much stronger and expensive denuvo DRM.
The real loss was in the inability to sell the 90% of titles I no longer care about owning, but that's already true immediately after purchase.
Steam shutting down and taking your library with it really doesn't change much except you lose that nice delivery platform with good integrations (achievements, workshop mods, multiplayer integration, automatic updates) for games you're active in. For the 90% you were never going to touch again it wouldn't be noticeable, outside the annoying reminder you were never able to resell them. The other 10% just reverts back to "pirate it" which is about here on my scale:
"find that legal physical copy to play with" < "pirate it" < "click button on Steam"
All (most?) Steam games have a very simple DRM that is extremely easy to bypass, and you can find examples on github.
However, a lot of games add their own DRM and/or protection scheme that complicates things.
EDIT: technically there are two distinct component: the actual DRM, called steamstub, and the steamwork library, that does not work without steam but it is not considered drm. Both can be easily bypassed/emulated.
I see, but there is Steam DRM there. So, I guess as the other commenter was alluding to, if Steam goes belly up so does your collection, regardless of the dev studio's intention (Or atleast, locked behind a DRM bypass).
I understood this in terms of Live Service games, but did not consider Steam's ability to shut down their own platform and kill my locally installed single player games with it (Again, I'm seeing its possible and seems easy to bypass usually, but the principle of the matter)
I tried to search if it's possible for a dev studio to release a game on Steam that works without it, by which I mean that if I uninstall Steam, the games keep working; I wasn't able to confirm, but it seems to be theoretically possible...
None of the games I have in my library work like that, but online some people suggest that some games work even without Steam, once installed.
Definitely not all games, and for games that do have it cracking it is in most cases as simple as swapping out a Steam .dll (so very easy). It's primarily there as appeasement for devs who would be reluctant to engage with a platform with no copy protection, or in otherwords is mostly theater.
I haven't tried with too many games since the usecase only comes up rarely, but I know that Downwell and UFO 50 work this way off the top of my head. They come with a Steam dll that will try to launch Steam for the sake of getting achievements and such, but if you delete them or just don't have Steam they launch all the same.
I am looking forward to the day when they shutdown and everybody realizes this.