the party attended Graz’zt’s party, ate food, got drunk, had sexy times with the “ladies”, and attacked Graz’zt.
After successfully dunking Graz’zt’s head into the scrying pool, Trogdor was ready to fight.
Graz’zt however was waiting for the attack to happen and instructed to “heroes” to wait a moment. he cleared the room so it was just the party and Graz’zt and his entourage. He explained his need for a messenger to hell and convinced the group to help stage his death.
This would make Iggwilv believe she was free and give the party the means to continue on through hell.