The way to get out with all dah shiney gold bars is with a stealth boy, super important to have one.  Or if you have PN installed, just get the assassin suit, PN gives it a stealth field that can be activated.  Anyway, once Elijah has been conviced to come down, activate your stealth boy and start walking, no sneaking yet.  Head straight for the building in front of you and don't worry about that turret above that entrance it detects you but will not trigger the barriers, once inside go right.  The goal is to enter the place with the elevator, but from the left side, rather than the right (wich is the side Elijah will exit out of.)  Now before you leave the building thing you just entered, crouch down and start sneak walking, because right above that doorway is a turret that WILL detect you, stealth boy or no and if it does the barriers go up so yeah start sneaking.  So once your past the doorway and clear to the elevator stand up and start walking, give yourself a pat on the back, eat a cookie, and feel super good about yourself because you just walked out with all the gold, and trapped Elijah in the vault.  Oh one last thing, there's a timer on this.  That timer is Elijah getting to the vault door, the second he reaches it the barriers will go up, even if you haven't been detected.  Oh and never try to go right by him, he'll detect you, always go around.