It appears that fallen lunatics spawned by Hellish Machinations aren’t (always) “deleted” when a player fails Echoing Nightmare through being overwhelmed. While they are easy to kill afterwards, it can still catch a player off guard (and lead to character loss on HC) since the basic idea is that once it’s declared that you’re done with the ‘rift’, there will be no more enemies.
On a related note, it also looks like fallen lunatics timing out and exploding on their own will add to player’s progress even if they haven’t landed a single hit on the mob.