It will still be hard tell. Sometimes there is someone playing a champion where it is their actual best option even if the entire enemy team is taking the nexus. Like if it is a garen or nasus top who dominated lane but the team lost every other inhibitor in 9 minutes while the score is 2-23.
It will appear as though that the player doesnt care, but them trying to defend the base will just result with him dying just as quick as everyone else.
There are other cases where the game is clearly over and nothing can be done to salvage it. 3 people are ready for the game to end, one person naively thinks you can win, and the last person just votes no to keep everyone else hostage. In these circumstances, I won't fault a thresh or braum support for afk split pushing so the game ends faster.
But then there are the legit circumstances where the game is even or you are winning.... and that one teammate has to go way out of their way to afk in a side lane with the intent to lose the game.
Now usually you can tell all of these scenarios apart from one another easily when you are in game. However, if you are Riot Support, you arent going to invest the time needed to confirm whether or not the player was intending to lose. Riot Support only acts on it if you do all of the investigating for them and provide the proof since they dont look into cases or context of cases. Even then, 1 game is often not a sample size large enough to motivate them to take action. They will usually only take action if you give them proof over many games. They are horrific at empathizing. Their excuse will likely be that they dont have time to look into the case that thoroughly due to high volume number of cases they have to deal with.
Which isnt a bad excuse..... but if that is their excuse then they compromise the consistency and integrity of even having a punishment system in the first place. Would be cool if they could hire people who give enough of a fuck to look into the context of every case.