Will Halo have bots?

No. It was recently announced that because of the nature of Halo's levels and AI, there would be no bots to play against in multiplayer game modes.

Basically, the AI that controls human and covenant units in the solo game depends heavily on information about specific encounters and levels for its behavior. They have no understanding of the game types and objectives in various multiplayer games like capture the flag or king of the hill, and as such would not make good opponents or teammates in those games.