Strange thing happened that I can't figure out. I began the final decent, Dragonborn side quest, a few wks ago. Early on, I decided I needed to level up more on my character so I left the quest at the point that I'd entered the mine shaft after getting the Quest and go as far as opening up the gate, then I decided to leave the Dragonborn area and head back to Skyrim for awhile. Well, today I finally had the amour and leveled up enough, so I return. Go into the mine and see that the old man, Crescius and his wife have left. So I head back into the mine and I am stopped at the passage where there used to be the planks barring the entrance to where the keyed gate is. The planks are gone (because I took them down before) but I can't squeeze through the entrance! What the---- ??????

I searched my journal, and the quest is gone! What could have happened?