Adventure Difficulty: I Like Peril

I'm writing my next micro-adventure, it's a low-level tromp through two encounters.  It's a treasure map adventure type.  I tend to make adventures on the tough side.  Some say too tough.  I'm a fan of peril.  I like to develop the feeling of danger, situations where the players are damned if they do or don't, and the awareness that death is a possibility.

The adventure that I'm writing, gravity is the real threat, the monsters (harpies) while dangerous aren't as dangerous as a 100' fall.  Here's the setting: players find a map, leads them a waterfall (I haven't named it yet) where the lost treasure of the bone soldier is supposed to be waiting.  A good old buried treasure. 

The players have to traverse a narrow path along a steep hill, where the path encounters the harpies is about 100' up.  The harpies are singing their song and lure their charmed victims off the cliff.  A little Wile E Coyote action.

I think it creates interesting scenarios.  If the charmed character attempts to walk off do the rest of the party grab him or attack the harpy.  There is very little room for failed rolls in this case.  A failed roll could result in a character's death.  There are many who disagree with this philosophy.  But without this kind of threat I think the adventure weakens and I lose my peril.  As I said, I like peril.