Because this is a Main Quest it MUST be possible to secure the key to go in the Mine and find the last thing you need for HOE Bound.

I played like this: take all the loot I can when I first came at the mine quarter, but
don't go IN the tower where the level 27 Black rings are (and the Guild Master to trigger that quest "Guild without a Master").
After I have my Battle Tower and I'm level 26 or higher I fly to the Minetower and rescue the Guildmaster William and he give me the key...
Maybe you can go the gate of the mine and try to go in?
Raze...?