Terraria multiplayer has a system where enemies scale with power according to player number. AFK players in the PvE dimension cause bosses to scale up in power, and sometimes a single player can be the tipping point for survivability against a boss.
A system that kicks players that have been AFK for more than 1 minute back to Rift should be implemented to counter this issue. Perhaps a seperate section in Rift could be made for this where the player is presented with 2 teleporters: 1 leading to Rift spawn and the other back to PvE.
(similar suggestion here, although it is outdated and more generalized: AFK Pool/Building/Other)