Hey, it's *your* era, too! :)
A game with multiple paths through, depending on the choices you make, is interesting. As long as there are clues throughout the game, to hint at the choices, I don't see a problem with it.
My point is that his game isn't unwinnable... or shouldn't be with just a few tweaks... but it is a game where you can get to a stage where you can't get the best ending. I think that's fine, as long as each ending is equally as fleshed out and satisfying for the player... Pixelman may want to check that this is the case and expand the ending text if necessary.
The rock, crystal and pick-axe aren't red herrings. The crystal allows access to the maze (at least that was the intention, the fact it didn't when I played it was a bug). The rock allows you to get the pick-axe, and the pick-axe is the tool that triggers one of the bad endings.
I'd say there just needs to be a little more sign-posting of the potential consequences of the player's actions, and a few tweaks to the puzzles to make sure there is always an ending available. It's definitely and interesting and ambitious game, given the Jam time-limit and framework.