I wouldn't call that very suspenseful... that's just a tease. The best suspense in Berserk is when Guts is in battle against an opponent many times stronger than himself and death or serious injury lurks at every wrong move.
I believe it is inevitable that Casca will die sometime near the end of the manga. Probably a long time after she is back to normal, when things between her and guts are finally starting to settle in. Casca's death is the only thing that could bring Guts into a feeling of hopelessness needed...
I would think something psychological manifests into something spiritual in the berserk universe. It is said that the spiritual realm is the human's mental world, where dreams and thoughts manifest into existence there.
Since were talking about Skull Knight speculations I had a thought of mine to share about him. I wonder if he's not emperor gaiseric, maybe void? This seems unlikely but the author has been known to throw a lot of interesting twists to the story. The skull knight hasn't revealed himself as...