Thank you very much. This issue has been formally submitted to the team.
And after loading up your save game, it looks like there is still a way you can access the Stronghold Dungeon and the deeper levels of Od Nua.
If you exit the Stronghold Great Hall to the Stronghold Exterior, then walk near the Chapel, there should be a cellar door on the right side of the Chapel. If you click on that, Accept your party, then scroll the map to the top, you should be able to transition to the first level of Od Nua where you had fought Maerwald. From there, you can use the stairs on the right of the area to go further down, or use the stairs in the top-right to go up to the Dungeon. I hope that helps you!