The Didact is most likely still alive, as his monologue in the final cinematic is clearly refering to events of the game; most importantly the sentence about how the Reclamation has already begun. This is about Chief's discovery of humanity's past and his accelerated evolution, which will probably bring him to something like the level of the ancient humans.
But there are other signs, like how the Didact's words about humanity being the greatest threat in the Galaxy are paired with the first shots of the Infinity's armor bay with hundreds of supersoldiers augmented and trained in just a few years. And Infinity itself is more than a match for the largest ships in the remnants of the Covenant fleet that's been in complete disarray since the Prophets' defeat. Humanity has managed to build this capital ship and a small army of Spartans in just a few years from their discovery of Forerunner technology and a war they've nearly lost.
This sort of justifies the Didact's worries, especially when you consider ONI's complete lack of morals and what they could do with a fleet of Infinity class ships and thousands of Spartans... And then there's the mentally unstable Spartan 117 who's just lost the most important connection to his own humanity. So the following Halo games could go to some really interesting places - I hope 343 will live up to the set-ups of Halo 4.
But there are other signs, like how the Didact's words about humanity being the greatest threat in the Galaxy are paired with the first shots of the Infinity's armor bay with hundreds of supersoldiers augmented and trained in just a few years. And Infinity itself is more than a match for the largest ships in the remnants of the Covenant fleet that's been in complete disarray since the Prophets' defeat. Humanity has managed to build this capital ship and a small army of Spartans in just a few years from their discovery of Forerunner technology and a war they've nearly lost.
This sort of justifies the Didact's worries, especially when you consider ONI's complete lack of morals and what they could do with a fleet of Infinity class ships and thousands of Spartans... And then there's the mentally unstable Spartan 117 who's just lost the most important connection to his own humanity. So the following Halo games could go to some really interesting places - I hope 343 will live up to the set-ups of Halo 4.