I doubt they will want to keep supporting a game they aren't allow to sell. Not to mention Bethesda might actually tell them to drop support for the already purchased copies.
Considering Bethesda already works with Steam, I don't see that happening.
But someone did post a snippet:
I can't speak for other digital distribution platforms, but games aren't removed from Steam. They may be removed from the store so that no one else can buy them, but for anyone who already owns them, they stay in your account, and remain available from the download servers indefinitely.
Which was my first thought as well.