With Didact dead (at least what the humanity knows so far) and there is no real threat to humanity and with great numbers of Spartan-IV’s available. Who needs Master Chief?
When you think about it, it all makes sence UNSC have retired Master Chief from the service. He is no longer needed in service specially with the great amount of Spartan-IVs. Yes. Spartan-II are superior than Spartan-IVs but the numbers makes up for that disadvantage and we also know the story of Master Chief will continue and that makes Halo 5 even more interesting. What will happen that will make Master Chief put on his Spartan armor again.
1.An attack on earth—but by whom? The Covenant are no longer a major threat. Requiem is gone and prometheans are extinct.Does that mean no more Promethens in halo 5 and 6? Maybe real forerunners Faber?..Flood?..Precursors? Something new (wink-wink Halo.CEA terminals)
Halo CE terminal 5 video link
2.Or Someone who has a personal vendetta against Master Chief –Didact?..Jul Mdama?
What also is an interesting plot to the Master Chief story is his confrontation with the librarian. She fast forwarded Chiefs genetic evolution. You can bet that ONI wants to know how Chief has evolved. Could Chief be going through same phase he went through as a child? When he was kidnapped and trained …augmentated and such!
How will Master Chief change…considering that all he ever have known is military service and now when he is not needed…surely it will change him .Also considering that he has also lost Cortana, his only true companion.
Halo 4 seems to be just an intro into the new trilogy and its characters. The way Halo 4 and spartanops ended pays the way for great changes in this trilogy and halo universe in generell. You bet Master Chief is getting a new armour 
Btw…sorry if some of you find my english to be lacking. English isnt my first or second language.
