I did 2 Athena voyages yesterday with 2 different crews. Each time we finished 1 or 2 islands and then all of a sudden 1 of our crewmates went AFK. One spent 2+ hours dead on the Ferry, "sleeping" behind where you spawn in. I watched him move every few minutes to avoid the autokick. When we finally turned in the Chest of Legends he came back miraculously. On my 2nd one, one person disappeared for about half an hour while we did one of the Gold Hoarder map islands. The entire crew was looking for him. We repeatedly asked, over voice chat and text chat, for him to respond using emotes, text chat or voice chat; something to let us know he was there. We eventually brig'd him when we couldn't find him or get him to help. He was active in the brig before going AFK. Once we were sure he was AFK, we voted him out of the brig (thinking he would autokick for inactivity) and he never moved but was never kicked.
There must be a solution for this. It's too easy for people to find themselves on an Athena and then go AFK. They know the rest of the crew won't abandon the voyage once it starts. They are abusing the system.