You mean the game that is the only place to play Combat Evolved & Halo 2 on Xbox LIVE? And now with the Halo 3 Brigade playing Halo 3-proper, we can actually play CE & Halo 2 Big Team? Regardless of whether or not those who leave the MCC miss it, I think I can safely speak for those of us who will still be playing the MCC by saying all the "Vote Halo 3 or I Quit" people who won't be missed.
That said, I too will be playing Halo 3 BC. I actually like all the games. It's the picky people who annoy me. But I'm planning on using the MCC for CE/H2/H2A and using the BC versions of H3 & H4. I think if everyone does that, it won't split up the people playing Halo 3 between the BC version and MCC. It'll also make the MCC a nice place to play the OG Xbox Halos. Though, I'm not sure if everyone likes to jump around from Halo game to Halo game like I do. You know, those damn picky people I mentioned earlier. lol