I wouldn't count on that game getting a proper DRM-free release. The DRM-free downloads from Humble only feature episodes 1 and 2. If you want all 4 episodes, you have to use Steam.
From the
developers homepage "Note that at this time, only the Steam version offers the complete game, but your Humble account has a Steam key attached to it that you can redeem." They say "at this time", but I doubt they'll ever bother to update the DRM-free version. The final episodes were released on Steam almost a year ago. That's more than enough time to update the DRM-free builds.
They've also removed the option to buy via Humble widget from their page.
As funl as the game is, the attitude of the developer towards DRM-free is something I don't want to support.