Based on the videos it looks like only one player needs to get over and DPS the boss's barrier down. If you go in with the Thancred Trust he'll always make it while going in with both Alphi and Minfillia results in both of them at best getting halfway through by the time the player and other Trusts make it and take it down.
The question of course becomes what happens if all four people keep failing to make it. Because you don't die when you fail, you get to keep trying but the boss has a cast timer. (Probably wipe)
