You dont need to kill him - theoretically. But that doesnt have any consequence in the game, as far as i know.

Which could be expanded upon too.
And probably will.

Its not about just killing him but expanding and pushing the story forward, by the two steps i mentioned - none of which was specifically killing Braccus.

As for two characters, ive been playing the game like that and it brings a different kind of a feel to it all. Especially in co-op.

Those that dont like that surely dont need to play this - assuming it ever becomes reality, of course.