Riot probably gets this a lot, this is a common concern of many players and probably goes hand in hand for staff. Ever since the Remake function has come out, a majority of losses due to players disconnecting have decreased drastically, however there a still few concerns at hand.
As an avid player of League of Legends for around 5 years now, it has come to my attention that there are still many flaws in the function that requires implementing in the near future. For one, players who have left the game along enough to be alerted by Leaver Buster, should allow it so their team could either remake, or have a reduced LP loss and no demotion if they are on 0 LP and require 1 more game to become demoted. In my case, I had gotten to about 32 LP right after making it to Diamond 4, right after, I had about 3 games, two of which had players which disconnected—in one of the games, I was lucky enough to remake, however in the other one, the disconnection allowed the enemy to take advantage of the situation and ultimately lose us the games. The player, although had reconnected, posed no threat and didn't change the outcome, an eventual defeat. In my most recent match which had gotten me demoted, the Anivia had disconnected for about 5 minutes, as a result Annie had roamed, gaining a whole kill and an assist. She had killed our jungler which had stopped any ganks that they could've made if they had a normal jungle clear.
If Riot is scared of the abuse of such function, then simply 'no demotion' if they had lost should occur or instead of losing a great amount of LP, it is cut by a percentage. And if needed, Riot should implement another system to detect abuse of the system if players do simply disconnect and then allow the team to have a cut amount of LP. This could also be avoided by having this only available to Solo Dynamic Games or if the person disconnected is not queued up with anyone else. Although it can still lead to abuse, the abuse would be quite minimal.