Bungie can no longer do Halo. They're signing on with Activision, and they're going to send new games across all consoles. Microsoft has exclusive Xbox rights to Halo, so Bungie can't do more. But they've made 343 Industries to work on the Halo franchise in the meantime. Halo's going to keep on going, just Bungie wont be doing it anymore. I believe there's a fair amount of people from Bungie working at the new place, but Bungie itself will not be making more Halo games.
Bungie has talked about making a Halo movie and how it'll effect future games, which insinuates future games, not to mention the cliffhanger at the end of Halo 3 and the one at the end of ODST. The Halo franchise will go on, Microsoft's not dumb enough to give it up quite yet, and the Halo franchise actually has a lot of potential, if they'd go to the other facets of the Halo universe. The fact that the Spartan IIIs aren't stealth based in Reach somewhat irritates me simply because they're giving up a massive opportunity.
Halo will continue, just not under Bungie's banner.
EDIT: And, yes, I am excited about it. The space combat just amped that up a lot for me.