Thank you for the suggestions Kvellen, and you are correct; I am playing in turn based mode. I tried what you suggested, specifically I loaded the auto save made when I enter the arena and before starting combat began by disabling turn based mode. I then fought the Tyrant without using any spells that dismiss it or any of the other summons made by the Tyrant. I focus the attack on the Tyrant, taking it down before then slaying the remaining summons. But still the game doesn't seem to react and the field is still up around the arena, with nothing available to interact with. Is there a way to report this to Obsidian along with a save file?