Thank you! The game is around 10 minutes so it doesn't make much sense for an autosave feature, but I agree that it's too punishing. For now, I'll slow down the boss, and ensure that sequence is more audible.
Fortunately, when thinking about solutions to your problem, I had a great idea that will fix the frustration and turn death into a meaningful experience - taking the player to hell, which they can escape. I may work on this as an update.