DC Leaver Status

So yesterday I was playing in a solo/duo ranked game. For some odd reason my internet decided to die for 10-15 minutes. I finally get back into my game and my team is losing big time, something like 20 kills down. We all banded together and I played a monster Zac game and we ended up coming back and winning somehow. Super proud we won and none of my teammates flamed me for my internet mishap. But when I get to the stats screen, it demotes me back to Gold 4 from Gold 3. How does this work? I came back, carried the game and definitely made up for missing alot of the early game. How is it fair that in this instance you get a "Leaver" and demoted... Kinda ridiculous if you ask me.