Your gear, your own responsibility. Unless it's on Riot's end (they'll usually implement "Loss forgiven" until it's fixed), it's on you to make sure your internet's working properly. If you know your internet sucks (or is sucking), your own fault for taking the risk by playing.
When you've made sure that it's working (and has been proven to be working fine) and it still cuts off, well tough luck there. The good thing is, that should be a very rare occurrence because if you had checked, you'd have discovered your net is acting up and shouldn't have started a ranked game.
If your situation was the second case, well, bad luck but you'll get the LP back some time if you don't purposely start a game while you're lagging.