Singed players generally have the least kill participation / % contribution but usually take the most objectives (turrets);
The best thing a player who is behind can do is either solo farm up while teammates stall for time (if a carry); split push/farm/get turrets (if tank/bruiser/top laner); or become a punching bag/distraction/cc bot/'suicide bomber' to take out an enemy with them in teamfights.
Just because someone has a bad KDA, or little to no kills whatsoever, does not make them irrelevant, useless or 'bad'. There are always ways to be relevant in the game and actually perform important tasks which might otherwise be be ignored by players with the "KDA means everything, must kill kill kill" mindset.
Players who tend to have that mentality and behavior in league often times grief/rage more from my experience as well, and rarely focus on what is important; getting the nexus. It's very possible to be an 'unseen carry' in the sense that your laser focused efforts to secure objectives or maximizing your champion strengths and abilities even while down in kills, means and contributes a lot more to the overall success of the game than simply just farming kills or trying to stay with a high KDA.
Call me crazy but, I'd rather try to consistently have a victory screen at the end of my games, even if I have to go 0-20 and take the turrets/inhibs/dragons/etc myself and die in the process.
Too often "KDA Warriors" lose sight of the real objective in league, and rather focus on "making those sick outplays, bruhhhh".