Well, it's just a different perspective- from Susan's perspective, she has no idea where they are, all she knows is that they all died, so I think we're very free to suppose anything we want about Susan's reaction to that. We see her as being left behind, but she would see herself as the only survivor.

I don't know that they had other friends; I don't believe it's explicitly mentioned, but I don't believe that, after years of diplomatic work and having very public lives as Narnian rulers, that they would tend towards staying solely a little in-group.