After finishing the game I had to use a previous saved game to continue. Is that the way it is? Not only that, but I went back to the Asylum and got trapped in there. You can't use teleporter and the outside door is locked. Please tell me i'm not screwed. thanks.

Once you initiate the final battle with Irenicus, the game is over. You either win or die, but either way that's it. If you want to explore further, do it before you hunt down Irenicus.