Erlang, FoundationDB, there's plenty of success stories of products who were EOL at some point and open sourcing was the thing that made them explode in popularity.

I think Fable is a very-high quality product, it's unfortunate it didn't materialize as a business, but the software has enough quality and popularity to maybe become something like the Blender of that niche; a thing that would be extremely beneficial to any of the founders' future endeavors.