[Bug?] Imshael

I encountered Imshael and fought without any potions. After dying, I reloaded my last autosave, which started me at the initial dialogue with Imshael. I exited the conversation and ran out of the area before he put up the barrier, I fast travelled to camp, was there for a moment, and suddenly I was transported back to Imshael, except I was UNDER the castle. Blackwall was fighting Imshael alone, I moved far away from battle so that my party re-gathered, then I traveled back to a camp. Now when I go back to fight Imshael, the barrier is still up. I am unable to move forward. I have done so much exploring since then that I do not want to go back to a previous save. Is there any way to re-set this battle? Otherwise I can't complete a major quest.

I've also had this issue, such a pain in the **bleep**, hours later still locked out

if you get your mage to go through the wall opening to the right of the blocked passageway and turn left, go right up to the wall, turn right and go as far as you can without falling off, turn round and you will notice the rest of your group has gone through the barrier.  Quickly swap to one of them and you will join them.

There is no guarantee Ishmael will be in there but he does eventually show up if you do it enough times....