Has anyone ever wondered: after Halo 4-6 are done, is 343i going to continue making Halo-related games? ODST 2? Halo Wars 2? Maybe a new trilogy? Or will 343i go in a new direction and part ways with Halo? Is making at least three new Halo games Microsoft’s attempt at milking the franchise?
It really is a good question. What does the community think?
Considering they were formed to take care of all things halo, I think thats all they will do. Hopefully, Halo will continue to be expanded upon and continue for a long time like star trek 
But if they can continue to come up with new ideas and story plots, Halo will continue to be a great game.
If it’s still financially viable to keep making new Halo games, Microsoft are probably (and hopefully) going to do so by tasking 343i with it. If not, 343i will most likely get disbanded and its members re-distributed to other Microsoft Studios teams. That’s what happened to Hired Gun, the in-house team that ported Halo 2 to the PC and provided support for it.
A quarter of them would probably be retired by then. Another quarter will find new things to do in life or leave from certain issues. The rest would probably make spin-off games of the Halo series… After they get new members…Probably.