that the ritual scroll you get from the Helmite ghost at WK has an expiration date? I didn't.
I wrapped up the whole of WK except for the very last step - choosing how to end the story. I had both scrolls, and since I wanted to use the keep as a storehouse, I thought (stupidly) that I would just hold onto them until ToB - not realizing that you can still access the upper sections of the keep even after using the scroll.
So, I get to the part where I am casually moving all of my party's stuff from the stronghold to the keep and, I notice a message saying that Odren's ritual scroll had disintegrated into dust, but I hadn't planned on using it anyway - I only needed the second scroll.
Right about that time, Aerie decides she is fatigued, and since we never get attacked at the keep, I hit the rest button. Amazingly, despite Meck standing right there, we were able to rest. When we woke up, however, we had a bit of a surprise. The imprisoned one shows up and wrecks the party like it's the end of the world. Being completely unprepared, I did the only thing I could do, and reloaded the last quick save. I figured I would just seal the place and be done with it.
Except it wasn't just Odren's scroll that disintegrated. It was BOTH of them. This was not good, and there was no way I was going to redo weeks of work elsewhere, so I... looked up the item code for the helmite ghost's scroll and consoled it in. (It's plot01q for the curious)
Amazingly, it worked. We got the XP, the lower level was sealed, and, thankfully, the upper levels were not. I was able to transfer the party's stuff to the cabinets in the room with Lum's machine.
All that to say, sometimes the sense of urgency is fake, but sometimes it's not.
Also, as an aside, what do you have to do to kill that thing? He was dropping so many high-level enemies right and left that we never could get a single hit in. I don't think Melissan was that bad.