We have some possible spoilers on story elements for Halo 5. The source is legit, but a lot of this is speculatory.
The information comes from official comic Halo Escalation, where Scruggs is telling Sarah Palmer that a conspiracy is afoot to hide Didact. This is what he tells her:
- The UNSC blames the attack on Earth on the Covenant Remnant, keeping Didact a complete secret.
- The Arbiter has not been able to make peace because ONI has kept trouble brewing. ONI has been funding the Elite rebellions, such as the Kilo Five Trilogy. This has been going on for five years now.
- Finally, Scruggs points out that Master Chief is nowhere to be found.
If we make connections between the information here and the apparent Halo 5 concept trailer, it appears that Master Chief has long been out of contact with the UNSC, and nobody knows where he is. The scenario outlined here is that Chief may have gone underground to undertake a top secret assignment.
As some other fans point out, the Chief may be on the hunt for Didact, which would explain parts of what we know from the canon. UNSC is keeping things about the Didact top secret so that Chief can eliminate him quietly. Chief may have deliberately cut communication to ensure his mission is a success. It’s also possible that Chief no longer wants to work with the UNSC, but is still committed to his mission.
Remember, again, this is all largely speculative for now. We will keep you up to date when more solid news about Halo 5 comes up.