The system that regulates leaves will not place a perma-ban on an account. However, the duration of an account suspension will dramatically increase the more frequently a player leaves.
So while you may start off with a 1 day suspension, before you know it, you could end up with a 7 day suspension.
If you were to ask me, I would recommend not attempting to play any LoL games on an unstable satellite connection. However, also keep in mind that the Leaver system only applies to queued matches, ranked games, and Co-Op games.
You can start Custom Matches and leave whenever you desire without incurring a leaver penalty.