He went to CASTLE base along with Dr. Halsey..after that..none is heard from himThank you, I don't know the answer to your. Please enjoy your beverage ( He probably went missing in action during the Castle Base raid..
What are you talking about? Jun accompanied Dr. Halsey to CASTLE Base, not the Master Chief. The Chief, at this time, would be in space, fighting the Covenant (read Halo: Fall of Reach and Halo: First Strike). Anyway, after the Battle of Installation 00 and destroying Installation 04B, the Chief and Arbiter attempted to escape their sure death by way of the frigate UNSC Forward Unto Dawn. The ship was already damaged, and when it jumped into Slipspace, only the front half (Arbiter's half) made it through, while the stern of the Dawn was left floating in space far outside of the Milky Way galaxy. The Chief entered cryo-sleep and told Cortana, "Wake me when you need me." As evidenced by the Halo 4 teaser trailer, the Chief and Cortana are both still alive and well, so not much time could have passed between the ending of Halo 3 and the beginning of Halo 4.