I'll add something else. It is a 3 or 4 months old anecdot, but I guess this is still how it works now.
So, during a ranked game, my PC just crashed. A shutdown, for "no reason" ( may be the heat, I don't know ).
I spent may be 10 minutes to reconnect, because it is quite slow to boot again, and the reconnexion didn't work at first, etc.
But, because I was destroying my opponent, and as my team was doing well, they were still totally fine in 4v5 during this time.
I finally managed to reconnect, after several tries, and we quickly ended the game as I was still "OK" in the game, due to the massivev advantage I had before my crash.
Aaaaand I lost 18LP.
Basically, if you have a PC problem, try your hardest to win a game, finally come back and end the game because you were so ahead of your opponent that 10 minutes still didn't allow him to catch you up, Riot doesn't give a fuck and will still make you lose 18 LP.
It didn't happen since this day, but now, make sure that next time my PC crash, I'll let it cool down, and I won't bother reconnecting. Why would I, if the result is the same ? Sympathy for my teammates ? Well, so bad, this is a team game where you're not choosing your team, next game they might be against me, a good strategy could be to tilt them beforehand.