Kitten update. We seem to be on the road to reconciliation. Yesterday we opened the barriers and let them mingle. There was a little hissing and growling, but no fighting. The turning point seemed to be when Thor cornered Loki and began licking his head. When Loki tried to hiss and run, Thor got him in a head lock and continued to lick his head.
Shortly after that, we found this:
This morning, I released the Thor and there was a little hissing when he rushed up to Loki, but a few minutes later I found Loki playing with a puff ball on the bed and Thor watching.
So I broke out the nip:
I think we are well on our way to a complete recovery.