My situation is pretty similar, but a little different. I am able to get to the point where I can talk to Durance about how I think Magran was allied with Woedica, but I only have 1 option other than "It's just a feeling I have". I've used all the dialogue options that aren't restricted like elfbarf, but I can't progress any further. The only quest I have left is this and the main quest.
Here's my save if it helps.
https://www.dropbox.com/s/t12h98e8k9wm3lg/1f124f8b937940438aeb013c704b4292%2025558615%20TheCelestialSapling.savegame?dl=0