Glad you liked it! The darkening effect was totally a last-minute addition, good to know it was worth it :D I'm also really happy you liked the difficulty, I was worried it might be too hard.
The gems don't respawn, but the money you have is left where you died. But yeah, the way the death mechanic works right now you can kind of get soft-locked if you're unlucky. I didn't manage to come up with a better solution, since I didn't want to have the player lose any money permanently. Respawning the gems might have been worth considering more seriously.
Lots of helpful feedback, thank you for writing this!