how to leave frostback basin

Please be aware that some of the things I mention may be considered Spoilers for those who haven't played the DLC Jaws of Hakkon

Just finished the DLC Jaws of Hakkon yesterday.  There is no battle with Ameridan, however, there are 2 major battles: 1-w/ Gurd Harofsen in the Treventer Ruins behind the Ice Wall, 2-w/ Hakkon himself on the coastline.

The first battle w/ Gurd requires you to defeat him before you can leave the ruins, I'm assuming that this is the battle you are referring to.  After defeating him you will meet Ameridan and be able to leave the temple.

The 2nd battle takes place outside, and you can leave at any time before you initiate it.

I'm not going to mention any more at this time, in case you don't want the spoilers.  If it's the Gurd fight that you're referring to and want some tips, respond the this thread and I can tell you the strategy that I used that might give you some help.

I beat him, but it will not let me leave the area and the cutscene never plays.  Not sure what the deal is but I do have Cass in my party and I have read that you cannot use her on any of the DLC.  Thoughts?  I even get the completed pop up for doing that part of the quest.  (Gurd Harefson in ruins).  But I cannot leave ruins and I never get the cutscene with Hakoon and Ameridan.

I have Cassi in my party most of the time. 

Never had a problem with her in the JoH DLC.  🤨