nope in red and blue, at silph co. tower, a man has a baby cubone, whose mothe was killed by team rocket.
so they dont die in labor, usually.
I think they just go to the cubone graveyard where all cubones go to die, and collect bones. either that or they excrete the mask as a liquid the liquid hardens into the bone mask they wear. or they savagly murder there mother, rip off the head skin it and dip it in bleach
it all makes perfect sense