Yeah no, this is a borderline terrible idea because of the implications.
AFKing is very rare compared to what you're saying, I haven't seen one in the past week and I've played a good 15+ hours, no way you're at a multiple over 50x my rate.
Regardless of that, voiding your loss is kind of pointless, it's like saying void a match because my teammate isn't as good as me or such, it devalues rank. If you're on a smurf, what's to stop you from telling your friend to not move, then you win the game? It's free painless wins. The other implication is a result of the other team not being barred from gaining points for the match - which we can all agree is reasonable and fair. In these systems, you can't have a point increase without point loss, or everyone would just MMR grind by a gentleman rule.
TL;DR This doesn't work in a ranking system and there's no way that AFK number is accurate/not greatly exaggerated.