They're holed up together at the Lucky 38. Earlier, I took a nap there, and when I woke up, ED-E and Boone were shooting at each other. Confused, I reloaded my most recent save, and that seemed to fix things. Now, a few hours of gameplay later, I came back to find that ED-E killed Cass at some point, and is trying to take out Veronica, Boone, and Rex. Reloading doesn't help. I can't talk to anyone to send them "home," because they won't talk to me while they're in combat. So I can . . . shoot ED-E, I guess, but I haven't finished any of the companion quests, and would sort of like to do that.
It's my first hardcoe run, so this is incredibly irritating.