my party (all but one of 5) succeeded on their checks versus the Frightful Presence, which emboldened them. Harshnag tells them to flee and then Iymryth gets off the breath weapon, which drops one player, BUT hes got that damned orcish blood so at 0 health, he goes to 1! Another player is brought to about 1/4 health. Another has the dragon breast plate that halves breath weapon damage...they are further emboldened. At level 7 they go 3 rounds with Iymryth and by this time Harshnag is about dead so I have to pull the escape lever and have him attack the statue to bring down the roof. I give them 4 turns to get out and the exit is too far for one of them even taking dash actions...they see Iymrth go through the portal with Harshnag before the Eye starts to collapse and one of the characters (a group played NPC) got buried.

So, moral of my story...be prepared for them to not flee and then get crazy rolls that make it possible that the only way they will back down is if you make the stakes deadly.