By the power of truth, I, while living, have conquered the universe.
No, Bungie ended the story of the Human-Covenant war in Halo 3. That was a small part of a much larger story revolving around the Forerunner, Precursors, Mendicant Bias and the Flood.
Given what Mendicant Bias tells us in the final Terminal at the end of Halo 3, he is sending John to the Forerunners as proof of his atonement. That ALONE opens up the potential for a whole new trilogy to continue where Halo 3 left off.