It was rumored that before the movie was cancelled, production costs were up to $200 million. Thats not HORRIBLE, especially for an epic film like Halo, but Microsoft also gets a 10% cut of the box office money, which makes the film look less attractive to studios who want to make some big money.
If somebody else took over, like Peter Jackson, who was the Executive-Producer
of the film, then maybe Fox and Universal would have been more willing to take a risk on the film, but they just didn't have enough confidence in the 'noob', Blomkamp.
Variety is reporting, "What happened was this: Universal, on behalf of both studios, asked for a meeting with the filmmakers just prior to the due date of a significant payment. Basically, they said that in order to move forward with the film, the filmmakers had to significantly reduce their deals. They waited until the last minute to have this conversation. Peter and Fran, after speaking with their producing partners and with Microsoft and Bungee (the studio that designed the original game), respectfully declined."
So is Halo over forever? No. Another studio could take over the film, and most likely will. But it might take a while. Pre-production on the film will continue.