I'm not sure, yes Halo 4 is made off of a redesigned version of Reach. It is also said that they're not in Matchmaking, which is not to say that they aren't in Custom Games or Forge, come to think of it, there was not much activity in Reach Matchmaking for Elites, a majority of the time you played as a Spartan, perhaps it will be the same, but without Elites. Plus, the Sangheili fleets have been together for years, I don't think it will be that simple, many that I have spoke with have said that they will retreat to Halo 3 or Reach, which will be the case. If you've been devoted to a cause for so long, it is near enough impossible to give up.