Solipsism works for a gaming universe.
It's independently verifiable and testable ... unless someone goes all real-world Solipsism, but, that's just circular reasoning. May as well say we're all in The Matrix and debate loses any point.
https://en.wikipedia.org/wiki/Solipsism
Then there's Plato's forms where the idea or form of something is more important than the physical reality of it.
https://en.wikipedia.org/wiki/Theory_of_Forms
... or something along those lines.
You could argue that, but, it's a bit of a weak argument in the espect that the social contract you enter into with the game is entirely one-sided, and there's also the whole limitations of verisimilitude in the "reality" of the game as well.
https://en.wikipedia.org/wiki/Social_contract
... and, shooting something in the head IS a relationship. Any interaction between two of anything whether it's physical, verbal, virtual, whatever is a relationship.
The subjectivity of the relationships in the game are another thing, as that's something entirely personal. It's the 4th wall.
I'll enjoy Fallout 4 as an immersive video game, but, to me, it's just a game. I'm not going to lose any sleep over anything in the game.
Someone else, however, might have a crisis of personality and spend a whole week trying to decide what gender they're going to play.
It is, however, just a game, and though it's meant to be thought provoking, and possibly present some moral dilemmas for some that haven't explored some of the thought experiments prevalent in some schools of philosophy, it's still just a game, and anyone getting too serious, and having way too strong an emotional investment in anything that has to do with the game might be best to take some time off and away from this kind of entertainment.
A healthy interest and participation in the game is fine.
Reading too much into puppet NPCs that are modeled for our entertainment? Eh, if it means that much to someone, then, to those it does, it'd probably be healthier to write a proper paper all about it for freshman Philosophy, Media Studies, or some other freshmen course at University than to get all OCD and give it more weight than it deserves.
After all, it really is just a game.