Getting demoted because someone AFKde on my team

I seriously think this shouldn't happen.

After a few bad games I ended at 0LP, I took a break and decided to try my luck again, everything was going well, we were winning, but around 25min our Mid laner, for unknown reasons, decided to go AFK, leaving us in a 4v5. After a 45min game, we ultimately lost because we needed the AP from our mid laner… I am frustrated that I got demoted because of someone leaving my game, I really think that there should be a system that makes it so even if you're already at 0LP, you can't get demoted because of a leaver.

In case you haven't noticed, I am writing this thread while being tilted beyond reason.