By the power of truth, I, while living, have conquered the universe.
Posted by: Cyco Halo Fan
Bungie has already stated the new IP is not another Marathon game, it's something brand new.
As for 343 nobody knows what exactly they are working on, all though there have been a lot of rumors lately about a Halo:CE remake. However I hope 343 does something entirely new with the Halo franchise, with the master cheif or not. As far as I am concerned the Halo storyline is over, but there is still so much more in the Halo universe anything could be possible.
Given that there are still 6 other Halo Rings, a still-active Portal Artefact on Earth and a Shield World housing some of Halo's main characters in it, I'd say Halo's story is far from over.