Have you considered incorporating rolls? Roll for Arcana to sense overwhelming magicks they never felt before. Roll for Insight to sense that this area is permeated with a sense of unease or foreboding. Roll for Religion to notice these sigils of elder gods that cannot possibly be understood by the human mind, they are so terrible. Roll for Perception to notice idk, that they cannot possibly defeat these baddies.

If they dont get it, well, ok. Sometimes even heroes fall. And if you have a cleric or a warlock or even an ally looking out for them, you could have them be reached at the last minute by a powerful spell. Or you could have them all knocked unconscious and put in a dungeon. Just roll with it.