i was pondering and then i just came up wit an idea. i think its a happy ending in the sense they all alive in gantz. and they continue their journey after beating up the vampires. and its open ending that they continue for years to come in gantz not living to go back to the real world because then they will lose their memory. so thenthey all live in gantz fighting 1 battle at a time
i also posted this on the mysterious poll thread.