I'm not sure what you mean Timmy, but Halo 4 is going to be a completely new game. It's a different company making the game and they can branch out and do what they want. So I wouldn't worry about the reach community getting smaller, because if Halo 4 is a game like CE, 2, or 3, then that group that stuck through those three games but stopped with Reach, will be back. They don't care the name honestly. They could name Halo 4, Sissys Rainbow Adventures, but as long as it plays good they will be back. No doubt the name Halo attracts people attention, but the gameplay itself is what makes up 90% of the fanbase.
So pretty much don't worry about Reach being not as fun as the other games, because Halo 4 will most likely be completely different and made by another company all together.