Same. Seems like there is no solution. I made the same mistake leaving this quest with hope that it will auto-restart. However, we should just load previous closest autosave. I played now more than 20 hours after this quest, so apparently it will be never completed by me (and you).
Or maybe in future there will be a mod that will alow us to fly through textures or so. I don't think that devs will fix that if it already happened.