So yeah, about that final boss. Tough little guy, innit?
I've noticed a few people dying midway through the battle, staying in and passing, but at the end not being rewarded due to being dead for too long.

The main reason why people don't just flee and port back is a cheat that instantly kills late arrivals. However, sometimes fleeing and returning is the right choice. Like I said above, if you're dead for longer than 2 rounds or so you don't appear to get drops from the boss.

The solution is as follows:
Coordinate with your team! If anyone has a heal, ask them to use it on you on the final round or a round or two before. If no one can heal, communicate with them to find out when they expect the boss to be defeated. You want to flee and rejoin no more than a round before the hit. You'll be defeated, but you'll have been in the circle dead for less than 2 rounds. I don't know if the minions give anything of value or if you get credit for them, but some loot is better than none, no?

If anyone has some more information they can contribute I would appreciate that. I haven't done this personally, only seen one other who did it under my advisement and it seemed to work out for him. I'm a death wizard so I can pretty easily tank until I can cast a scarecrow or Khrulhu so I almost never die.