I hope they don't ban you for that. Anyone who's that stupid to not appreciate the carry and still take it for granted deserves to lose. I do it all the time. I dominate mid, gank do everything and they farm let me die and I just say, "Hey all mid now or I just afk" and it's that simple to AFK and do something else.
I don't care about wins or losses or KDR or goblin coins. It's all about the fun of the game and playing it properly. So dumb noobs who think they are doing something when really you are just carrying them all the way don't really deserve to win.
Cheers
-JaySongs