"What, you don't think we could have taken you? Such little faith." Istredd is joking, since there is no change in hell they could have. The monster and Lucifer together would've done more damage than anyone could have prepared for. He has no idea what Thorne would do with them, although it seems most likely they would have put Lucifer down.

It didn't happen, that's the important part.

"I wish we understood more of the arcana. I don't think Urianger nor I have come up with much. For the beasts to come in with assigned arcana of their own ... it's interesting." Horrifying, sure, but interesting.