It is NOT against any rules to MPK an AFK player. ESPECIALLY when they are inside the bounds of a reive battlefield. You need to be harassing them or interfering with their gameplay for assisted player KO to be considered as MPK, and AFK players do not have any gameplay.

I mean, think of the abuse... go AFK right on top of a lair reive target (like Avian Roost), and the moment someone attacks it, you call a GM on them for MPK! You went AFK in the wrong spot and got killed? GM the person that started the fight! Someone accidentally hits autorun and is forced to retreat from the reive with 4 annoyed birds in tow, who then attack you as the nearest target because you didn't move? GM!

There are less severe measures to deal with AFKers though. In many cases, you can use the knockback AOE from mobs like Tulfaires to knock them out of bounds. Often the places they hide are also the places you would pull a mob to kill it without risking more agro or links, after all.

SE could fix the whole thing by not granting reive status to players that are in within reive bounds when it starts.