The 5 Apostles walked through the portal with some missing memories. They remembered Ning most of what happened, or so they thought at least.
They remembered the beasts they fought and even the dragon that appeared. Then they remembered Ning punching that dragon and then… was that how it all happened.
They didn't really have any reason to get suspicious of their own memories, so they walked out without a problem.
Ning was about to walk out as well, but he sensed that the space in there was about to collapse. He didn't know what would happen in the case of such spatial collapse, but he was sure that if that were to happen, the beasts in here would certainly die.
Now, Ning didn't care for the beasts that were in there. But he cared about the SS-ranked Mana stones inside the beasts. After all, this was the first SS-ranked dungeon in the world, so he had to get the mana stones.
Otherwise, it would be a waste to leave without them.