Riot doesn't give Loss Preventions unless the issue is serverside. There was maintenance on the servers in the last week, but ranked queues were disabled at the time so I do not think Riot will cooperate even if your game coincided with the general timeframe of the maintenance. It sucks and sounds a bit like your team was drophacked though. Another option is if you were playing with the party over LAN and there was a local network bug.
I don't know how to prevent that kind of problem, but if you do suspect you were drophacked I recommend you start recording your games with some sort of screencapture program like Xsplit so that you have evidence of the DC. I've never used a replay software for League but that may also work for collecting evidence.