Honestly thought if that's whats gonna happen, like is that the reason we've never heard of any of these people besides him? That'd be so dark.
I think he definitely ends up killing Krennic (Mendelson's character) and probably one of the main rebel characters.
Pretty cool that Genevieve O’Reilly played Mon Mothma in the prequels (Ep 3 - deleted scene) and now again in Rogue One. But yeah, they need to make Vader look ruthless. Shame Ian McDiarmid isn't it - regardless of whether Palpatine is.