Load you save from
Instead of waiting in the vault, head out to the left and then retrace your step through the vault. At this stage, you should be pretty much half way through stage one of the previous guide before he starts throwing a hissy fit. When you get to the overlook of the vault, turn left and the entrance we entered the level from is there, once outside of the vault, the trophy unlocks , leaving Elijah to his fate. Make you way back to the fountain.
At this stage we can leave the DLC, but you cannot return to the vault after completing it. When we exit, we'll get all of our stuff back from before the DLC. If over encumbered. At the top of the stairs, next to the ladder out is a box, deposite the heaviest items in here. Go to Gun Runners (or Gibson's scrap yard, she always seems to habe 29k caps on her every three days on my game) and sell the gold returning to the Abandoned BoS bunker to get your stuff back.