Not including Forge would be the stupidest move they could make. Given that its become a staple of the Halo experience, along with Firefight, it would make no sense for it not to be in Halo 4. I can see a reason for FF not to be included, as the enemies that are included in H4 may not be entirely compatible with the way it works (remember, we dont know who/what we'll be up against), so theres that. But unless Bungie have copyrighted Forge and its concept, which I doubt, then I can pretty much guarantee you that its not going anywhere. I just hope 343i listens to the community and changes/implements the things that need to be changed about Forge and Forgeworld.