If you manage to partition all your new update files in a separate RenPy archive (.rpa), then you should be able to just distribute that as the update.
I am, however, not sure how you should handle updates to already existing files using this method. Perhaps things can be redefined if they are...
This doesn't surprise me at all. I never expected things to last "back in the days" either. Too many things that can change, other than hosting/dns changes.
Game is worth checking out. The models are great, and the animator clearly spent some time on the animations. Story is fairly meh but passable. The girls do suffer a bit from having the same face though.