Unless things change with Microsoft, which is possible, I think they are the least necessary because of their relative lack of first-party IPs. Even if they dropped from the console market, I have no doubt Halo would continue, at least on PC--which, honestly, would be my preferred way of playing it, regardless.
However, I think Sega should stay as a third-party publisher. From where they're at, they enhance the other consoles, which is good for gaming. It would hurt both Sony and Nintendo to lose them.








