Just Wondering

I was watching t.v the other day and I was just flipping through some channels. And I kind of landed on this movie that was on Sci-Fi ((if anyone knows what channel that is.?)) but anyway there was this movie that was playing and it kind of gave me an idea of a new story. I'm not that sure if I should start writing it or not so I was asking for people's input.
The story is about this 17 year-old girl whose best friend is her 34 year-old dad. The girl's mom had died at the age of 16 when she was giving birth. So the girl's dad and her are incredibly close and they both mean the world to each other. But pretty soon the dad's world crashes down when he learns that he has to give up his life in order to save his daughters. You see, Death comes down to earth in a 19 year-old boy's form. And his job is to take the girl with him. In other words, her time is up and she is supposed to die. But Death thinks that she should live longer since she's so young. So instead he decides to take the father so he can take her place. The dad agrees but asks for one week to spend with his daughter. However, during this one week time period, Death starts to gain human feelings for the girl. He starts to realize that he's a monster and he killed millions and it's not the girls fault that her mom died. She didn't kill her mom, but he did. He kills everyone.
It's really confusing but when I was thinking about it yesterday night. It made more sense. Can you just ask me questions about it so I can answer any of them that you aren't sure about? Thankzs.