Players that suddenly leave the game + Loss prevention

There was this ranked game whereby, at the 5-minute mark, my mid laner Talon got ganked by the enemy jungler Vi. From there, he just left the game, never spoke a word, and didn't return to the game ever since. Are we right to receive a loss prevention, or this has been an issue for a long time? Temporarily/Permanently banning that player who went AFK for no reason is not as valuable compared to the other 4 players who lost due to 4v5.