The ONLY reason I ever leave a game is if
1) My parents call me for something
2) Said parents give me a chore when they call me.
3) The bathroom, obviously.
4) It's time to eat ( And my parents aren't patient with LoL games when it comes to eating time)
Even if I DO leave, I ALWAYS try to come back. I mean my last game I had to go eat and when I came back ( Because I DID come back) I got banned -.-. I don't think Riot thought about these points when they made the rule.
2) LoL games are a time commitment; check how much time you have BEFORE you join a game. Talk with your parents about chore assignment. Most parents are reasonable enough to give you a list of chores with due-dates. As long as you actually keep up and do your part, most parents will also be reasonable regarding "Hey, I'm about to start a 1 hour game with no pause... cool?"
3) LoL games are a time commitment; check how much time you have BEFORE you join a game. It's understandable that some people have bladder or intestinal disorders; but if you must live with such a horrible ailment then you should already know various tricks and workarounds. If you honestly can't make 60 straight minutes without a bathroom break, you may wish to consult a doctor.
4) LoL games are a time commitment; check how much time you have BEFORE you join a game. It sounds like your parents are the kind who like to have "sit down family dinner" time. This type of dinner usually has lead time on it. Speak to your parents regarding when you get notified about the time dinner will be at.
TL;DR All of your reasons sound like you simply have no sense of time management and no respect for other players.