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"