That's the scary thing, Elijah came there completely fucking prepared for what he was about to encounter. And he fucked some shit up for an old man. He was like an elderly technophile Batman with a Gauss rifle.
Honestly it always kinda sucked that you couldn't talk him down in Dead Money. It would have to be hard, like Lanius at the Dam levels of hard, but they really should have given you the option to reason the old fucker into fucking off or maybe even agreeing to work for you. He could stay i the old BoS bunker and cook up some shit for you. Come and visit from time to time, he might have chems, he might have weapons, or armor, or ammo, or something worth your while.
Yeah, I know you can't talk EVERYONE down, but if you could talk down someone as crazy and violent as Lanius you should have no problem talking down someone as crazy as Elijah.
And I will again bitch about the fact that you couldn't reunite Christine with Veronica. That was some fucking bullshit.