Personally I would, and I think they would have enough man power to work on Destiny and work on Halo at the same time. And I would much rather see Bungie and 343i co-develop the game together to keep new and old Halo gamers to stay.
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No, the MM for lolReach and Destiny was garbage and I wouldn't trust them to make a decent Halo MM given the direction they've taken since ODST. 343 have given us an excellent Halo MM with H5 (best since H3 by a mile) and I'd rather they keep making Halo games :)