Everyone is looking for a way to abuse the no lp loss if there is an afk... but no one is looking for a solution. Dont just say the OP's idea wont work, and then leave it at that. Give him a solution.
That being said multiple people have thought of this idea and you are not the first, OP. First of all LP is very stagnant and not a good indicator of rank. MMR is a better system to adjust when trying to compensate for unfairness. Now you see Rito with their "algorithm" has a specific formula that awards you a certain amount of MMR for winning based on your teams average MMR vs the enemy's teams average MMR. Similarily when you lose, mmr is taken away based on the average mmr of the teams. I have written to riot asking them to Punish Leaver's MMR extra or reduce the MMR lost when you have a leaver on your team.
They replied - Our mmr system is very delicate and adjusting the MMR based on a leaver would cause INFLATION or DEFLATION of our system. For every 5 players awarded MMR , 5 players has to lose MMR to keep the system balanced.
Now, i disagreed with this is many ways cause this means when you have a leaver on your team and you win the 4 v 5, the leaver is actually Awarded MMR. (you just cant see it cause league only shows lp)
so i would assume messing with lp or mmr would cause inflation/deflation of the system by riot standards (which i certainly would petition), but they would not change. so the only real solution is to create punishment on First Offence of leaving. Idk why league forgives first time offenders of afk. literally allowing millions of people to afk multiple times for free. Punishments do not have to be harsh, but there should be a punishment. I would give 30 minute - 1 hour ban from ranked que on first time offence and longer on more offences.