The lights are on
There seems to be this idea going around that 343 is full of ex-Bungie employees. This is false. In reality, there's only like 3 or 4 total people from Bungie. Everyone else, well, isn't.
Although I do believe Halo is still in good hands. 343 actually cares about what's going on in the Halo Universe.
Hopefully those 3 or four people worked on the story for the other Halo games. then all 343 has to do is work with them on the story and get the scope and magnitude of the levels right.