Please keep in mind that leaving games is not acceptable behavior in League of Legends. When you leave a game, you put your team at a significant disadvantage and likely ruin their experience. For this reason I recommend having at least an hour of time available before playing Summoner Rift. (It's rare for a game to last an hour, but it can happen on rare occasion.)
We know that from time to time despite your best efforts you may need to leave a game for a reason out of your control: emergencies and internet/hardware issues happen to everyone at some point. For that reason Leaverbuster doesn't punish you for a rare leave. As long as you continue to play more games without leaving, your account will be put back in good standing again. However, repeated leaving is not permitted and will lead to increasing punishments.
Just keep playing without leaving and you'll have nothing to worry about