Since Steve Downes has retired already I’m going to assume that Chief won’t be in Halo 6? I mean, they don’t have a voice actor so they can’t possibly include him in any sort of role except a silent one.
I highly doubt they’d hire a new voice actor to play Chief, that would just be shooting themselves in the food, missing, and taking their whole leg off.
At least this way 343 can get what they want and replace Chief with Locke.
They can’t have possibly recorded all of the dialogue since they’ve said they don’t even have a script and only have a “good idea” of what the story in the next game will be.