Discovered another reason why this mission might not be completed. The other day, a friend of mine sent Godric to Nicholas right in front of me. Everything was normal. Nicholas arrived. But then, a message appeared saying that Daleb had killed him. Agrail just stood by. And that was it.

Okay, my friend had a save before the assault on the garrison. He loaded it, and before Godric left, Isabel drove all the demons into the castle. The mission was completed.