Without the addon there was a robot companion that would refuse to go in, just like Fawkes does before you get the dlc. After you get the dlc both companions will go in, and be fine afterwards, because radiation doesn’t affect them.
Much like Fawkes the robot companion said some BS about not robbing you of your destiny before you install that particular dlc.
I understand this was/is a joke. That being said, Topsy may have a slightly differing opinion on that.
Edit: I made friends with the RBB&BC elephants before they were retired. I only interacted with them 4 times for less than a week at a time before they were retired. When I visit them in Florida, they know who I am and act like giant puppies whenever they smell me near. I have a particular love for elephants and orca.