Honestly, neither do I. Simba wouldn't leave, if anything, he'd only step down his reign to Kiara's, but live in Pride Rock until he dies. When Mufasa said "the sun would set on my time here", it mean't when he died, not exactly when the sun would set. Another thing, babies don't fall when their born with a "thump". That was just ridiculous. I also think she'd notice that the child is sticking out, that was way disturbing. By what you described the child birth, you are clearly underaged.