To a lot of people, Master Chief is Halo and vice versa. If it was any different, then 343i wouldn't have made this announcement:
343i Acknowledges Halo 5 Storytelling Mistake, Will Double Down on Master Chief Focus
Like Frankie said in the article, people have become attached to him over the last
fifteen 17 1/2 years. It's not going to be easy to get rid of him and I doubt they are even considering it for Halo: Infinite or getting rid of him in general. Unfortunately, Steve Downed will also not be arround forever, so that will be an other very sad day.
Anyways, the Halo Universe has so much to offer and I'm sure there are many stories left to be told that don't involve the Master Chief. They just have to explore other options and see what works and what doesn't, which will probably be a pretty hard task. Personally, I would like to see crazy things like them going all the way back to the Forerunner vs. Ancient Humanity vs. Flood timeline and see what they can do with that setting. Just one of the many examples out there.
We don't know if it's a conclusion, but it's definitely a sequel that takes place after Halo 5. That has been confirmed.