I don't see any reason why they would be removed and I don't see anything on Steamdb, but I can't seem to find either of the Afterfall games on the Steam store, and clicking on the store page button for either of them just takes me to the main Steam store page.
Still available to purchase on sub-pages:
http://store.steampowered.com/sub/43707/
http://store.steampowered.com/sub/27570/
http://store.steampowered.com/sub/18432/