Based on the OP, it would be hard to tell immediately why the patient crashed, they could have had a bleed, septic shock, heart failure, I mean who knows. However I must ask, if the patient was in PEA, why did you give succs? according to your post the pt was already dead. This reminds me of a time I went to a code on the floor and primary RN said pt is in Asystole and charged the zoll, she was quickly asked to leave the room. Another time during a code the pt's belly was about to blow and I warned my coworkers, the PA running the code offered us Zofran...she was also asked to leave the room.
I think your ER needs to run some mock codes TBH. You don't give a paralytic to a patient that's already dead, honestly an RN should have caught that and stopped the MD. Other than that I wouldn't stress it, sometimes its just that time.