Quit -blam!- stalking me you weirdo.
Hello guys! I have an interesting theory to present here, and it is that John- 117 returns to the hands of the UNSC.
To understand this, you first need to see the view point of ODST and Reach. A large part seems to be told through helmet feeds, and camera feeds, with some parts at free cam.
I will explain the free cam parts later, but first, the camera and FP view parts. These could all be reconstructed by ONI, which may explain why there are days missing in Reach.
The free cam parts, with no equipment around, is what is different. Being observant, you can tell that when it is John- 117, it is always this kind of cut scene.
So, my theory is, that Master Chief must be around some time later to tell his story, or Cortana (However unlikely, due to impending rampancy, and her time away). So, by some chance, MC lives on to tell his story, or it will just be a huge over sight by 343.
I guess only time will tell. Does this make sense?