With Halo 2 servers going down pretty soon, it seems reasonable to fear what the expiration will be on Halo 3 once Halo: Reach comes out later this year. According to Bungie, that’s not something we should really be sweating. Community director Brian Jarrard allayed any possible concern saying, “I think it would be safe to say we wouldn’t be investing so much time into doing massive matchmaking updates and then just turn (Halo 3 online support) off and walk away from it.”
He elaborates saying that they naturally want people to play the multiplayer in Reach, believing “it represents all of the good things from Halo 3 but better and more so,” but are aware of the hardcore players and pros who will likely take more time to transition than most.
To the point, Jarrard simply “can’t imagine” a world where the two games can’t coexist.
It doesn’t seem like anything to fear anyway, considering that Halo 2 is getting the plug pulled nearly a full five-and-a-half years after its release, and about two-and-a-half years after Halo 3 came on the scene. So it would seem there is at least that much time before even the possibility of any end to the game, but I wouldn’t be surprised if it went even longer still.