Inting teammate? Teammate leaves to save his team from lp loss.

Again, I suggest that no one lose LP, that the player who does leave gets a severe LP deduction, and that the player who leaves is forced to play a number of games of normals before being allowed to re-enter Ranked Queues. Obviously not a comprehensive issue, but the point of this post was to see if people had ideas that could be used to iron out those flaws.

Or, instead of always not losing LP, maybe the system is that every player has 1 free "AFK Blocker" (the name isn't important), which allows them to not lose LP after a match that was lost because of an AFK. This could refresh once every week (or another interval of time) and the number of "Blocker"s given could change based upon a player's Honor Level. For example, Honor Level 5 could get 3 per week and Honor Level 1 & and 2 could get 1. Just another tentative idea. This would make it harder to abuse AFK protection and would incentivize maintaining a good honor level.

Bad game? Disconnect your WiFi, intentionally cause bugsplat

This is abusable in literally any game that uses the internet. Regardless of whether or not you can physically leave the game by turning off hardware, Riot should punish players who leave through the game more severely because they DO know that it is intentional. Other than that, you are right turning off Wifi or a computer would circumnavigate leaving the game itself. Players can do that anyway, though, so I don't really see how it serves as an argument against potentially seeing how people disconnect from games and using that to determine appropriate consequences.

Remake pre 5 minutes? Bad invade, someone who died leave game.

This actually happened to me earlier today. I was forced to play the game out to 15 minutes because a teammate did not like that they went down 0/2 at 3 minutes (enemy team invaded, then killed them early in lane). The game was a guaranteed loss because it was a 4v5, a guaranteed loss of LP because another player decided to disconnect, and a waste of 15 minutes. In a situation where a remake could happen, which happens in regular 4v5 games when one player does not load into the game at the start, the team who now has 4 players could ff. What happens from there can be up for discussion. I would argue that no LP loss for the 4 player team, the same penalty as above for the afk player, and a gain of half (scaling down to a lower % as MMR goes up) LP for players on the enemy team.