No. MySims Agents (Wii) has a **linear, story-driven structure**. Once you complete the final mission and watch the credits, the game **ends**. You are returned to the main menu. There is **no post-game free roam**, no chapter select, and no way to re-enter the Temple (HQ) or any previous area.
If you want to revisit the Temple, you must **start a new game** and play through to that point again (~2–3 hours).