I would imagine all of the Halo assets default to Microsoft instantly and it would be entirely up to them to sell them again if they see fit. Although I think some of the Halo models were contracted out because they were plastic and Spartan doesn't have the machinery to do in-house plastics.
The question of the value of the DW and FSA IP is pretty open. It clearly has a solid, if very niche, market and it doesn't have much for direct competition. But the thing about gaming systems is that most developers have way more ideas than they have the ability to make them (see Spartan...). So I would wonder what gaming company would buy someone else's dead baby when they have many ideas of their own that they haven't got out yet. A lot of the initial work is done, but it would be hard to put your own spin on the system without destroying what value the IP has, the existing players. Change it too much and it isn't the same game any more, but leaving it the same would make it harder to embrace it as a developer.
Just the ideas from fans on the forums you could see a dozen different direction the game could go if they had their say.
Of course you have some miniature makers, such as Reaper, who are really just in the business of making models and not having their own game systems. They make generic models in certain genres and let the players do what they will. There could be some value there for them.
I could also see someone like Catalyst Game Labs take it, they tried to make a game called Leviathans, which seems to be pretty much dead, but a similar theme. But it is hard to say if that would be a good direction or be at complete conflict.
As an aside to all of that, I would be interested in working through a community based set of rules and ORBATs. The main issue for me is that while I've got a pretty good idea of game theory and statistics and technical writing, but I just don't have anyone to play with so couldn't do much for actual playtesting.
