Interestingly, when we played quest 12, the Heroes split up and the corner trap was not triggered until the wizard went back towards the stairway. Since the other Heroes were so separated from him already near the witch lord, I had it collapse behind the wizard who still had easy access to the stairs. The Heroes found The secret door in the first room immediately and went that way instead of towards the falling block.
I chose to not have the corner trap be disarmable in favor of it being part of the plot line. In a way, the witch lord can act as a second falling block trap through which the heroes have to navigate with veil of mist and pass through rock... Which they did, to my surprise.
I plan to not allow the falling blocks in quest 13 to be disarmable or searchable. The Heroes pretty much have it as a cakewalk at this point in the game. It certainly makes it more fun. they skipped all the traps in quest 12 not even bothering to explore that area of the board... However I think I goofed by telling them that the spirit blade is not in this quest. Had I not told them that, they probably would have explored the trapped areas.
However, if we weren't to say the spirit blade isn't in the quest, I probably also shouldn't even be disclosing the witch Lord stats or how many spells he has...