But I wonder.. would they have tried if they had a clear and easy way to grab Magnus and sever/transport him? I get the impression they would have just left him there.
Well, I think if Janeway had known that Seven's parents were right there and that there was a possibility of severing them, then she would have attempted to try. But Seven herself was clearly angry that her parents caused her to be assimilated (I mean...they did bring her on a ship and set out to study the Borg with a child on board. I would have been pissed if my parents put me in danger like that too). I think Janeway would have wanted to sever her father (not sure if her mother was there or still alive?) and re-humanize him and bring the family back together and all that, and I think a part of Seven would have wanted to sever him also...but I'm sure a part of her believed they deserved what they got.