The main series
- Was the detonation of the second Installation 04 powerful enough to destroy the Ark permanently, or will it eventually repair itself and rebuild the installation, possibly with Flood still on it? Is anyone planning an expedition to find out?
- Can we really say the story of Halo is over when the Halos themselves are just as much of a danger as they've always been, just waiting for some fool to fly in and release the Flood or activate them? Are we supposed to just take Thel 'Vadam's word that the galaxy's been made safe? Couldn't we have had a time skip to the demolition of the last known ring, or the incineration of the last known Flood specimens or something like that?
- Does the post-credits scene of Halo 3 take place at the Ark's location or somewhere else? What kind of beacon does Cortana drop, and how many years will it take to reach someone? Will the Chief wake, and if so, when and where?
- If he does wake, will he make it back to Cassandra? Does he want to?
- Doesn't the Flood's extragalactic origin mean they should still be at large out there? If they're not, what happened to them? If they are, why haven't they invaded our galaxy again?
- The heck is with all the contradictions on the numbers of Spartans and Spartan casualties?
- What's the nature of Gray Team's mission in Fall of Reach? Will they ever return from it?
- When will the secrecy around the history of the Spartan-IIs be lifted or broken? Will heads roll when it is, and if so, whose?
- Will major unrest result? If so, what side will will the major characters so far end up on?
- Will Cortana succumb to her seven-year lifespan or find a way to outlast it? Or is the seven-year lifespan being considered non-canon?
- Will the survivors of Ghosts of Onyx ever escape or get rescued from the micro Dyson sphere?
- What happened to Randall in 2532?
- How did John carry over 200 missions against the Covenant at the time when the latter had nearly total space superiority and no reason to fight on the ground?
- Is James dead? Will an effort be made to locate his body now that humans and Covenant are ostensibly at peace?
- What's the proper plural: Forerunners or Forerunner? Or are both equally accepted?
- How was Halsey able to contact Earth from Gettysburg in the Halo Graphic Novel, and why was she so determined to keep it a secret?
- Will anything come from studying the remaining fragments of the Reach time crystal?
- What was the Reach time crystal's original function?
- Roughly how do the Halo array, Forerunner teleporters and the Reach time crystal work? What else could be done with that technology?
- What could possibly have led Maria-062, a Spartan taught from childhood to regard duty as the highest good, to decide to retire in the middle of a war?
- What's the meaning of the Coral and Sacred Promise segments in Conversations?
- What's a Sharquoi besides "very freaking dangerous"?
- What's with the backwards message in Halo 2?
- At the end of Halo 2, why did the Forerunner dreadnought jump to a point so far from the Ark portal? And on that subject, how fast is "near relativistic speed"?
- How fast is Ark portal travel?
- What was Cortana's secret that Gravemind talked about?
- Why didn't Gravemind expect to die after the second Installation 04's firing? Is his mind spread wider than just the vicinity of High Charity?
- Did the entire remaining Covenant military accompany Truth to Installation 05 to eventually be destroyed at the Ark, or did some stay behind and survive? Do planetary outposts remain that could develop into a threat? Assembly's flavor text suggests a yes to at least the latter.
- Will the Covenant Separatists remain an organized force, considering that opposing the Prophets seem to have been their only common goal?
- If they do, what will they call themselves? What will they do next, besides ferrying the Elites who want to return to Sanghelios? Will they be effective as a permanent peacekeeping, Flood-exterminating and possibly Halo-demolishing force? Will they be able to control Journey believers within their ranks?
- If they don't, who will end up in control of their fleet? Will any of it end up with good guys, or at least guys favorably disposed to the UNSC and Sanghelios?
- How much was kept secret during the war that shouldn't have been? When were the Forerunner(s), the Halo network and the Flood first learned of?
- What year will the survivors of Halo Wars finally make it back to civilization?
- Will the Kig-yar make a bid for power now that the Covenant are at least weakened?
- What's the significance of the Legendary Planet's dramatic introduction in Halo 3? Is it something besides just another empty Shield World?
- What happened to the Precursors?
- How did the Flood originally come to exist?
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