Thank you so much for playing! As for your questions:
1) Yes, but that's been changed in the most recent release (In Too Deep by rice (itch.io)) where I also fix your losing track of oxygen problem
2) No, but I wanted to add some critters that glow a bit, so they'd help if you were out of battery, but they would chase you and if they hit you, you'd lose oxygen as if it were health. You'd be able to outpace them if you had stamina, and they'd run away from you if you shine the flashlight on them. I haven't gotten around to implementing it, I'd probably prioritize building the map up more.
There wasn't much down in the depths, just some glitchy triangles to make it feel voidy, and the old diver sprite and an unused fish sprite to fulfill the Memory Lane wildcard. If you get all the way to the bottom, you'd hit a win screen that says "You've entered the void. (You won?)" and you'd get softlocked in that scene.