Concerning Halo: Combat Evolved, Halo 2, and the Forerunner Saga, these stories needed the comfort of a Halo installation to drive their stories. It wouldn't feel right without them. The same cannot be said for anything else. Halo 3's Alpha replacement felt like fan service for the Halo faithful.

Halo has matured to a state where we really don't need to step foot on or be in orbit of one ever again. I don't think we've ever really needed them to be frank. Star Wars is still what it is without grand space battles, Battlestar Galactica still cherishes human drama when following the Cylons, and let's be honest, Stargate episodes focusing on gate malfunctions were dreadful.

With that said, when appropriate, Halo installations still need to make a grand appearance every so often. Not like a simple port-of-call, but an event of great wonder, novelty, and circumstance. Multiplayer and Firefight levels need not follow this. Anything wacky the Forerunners got up to in their spare time should be presented in this environment.