Sure. But Microsoft, as the publisher, determined giving Bungie the manpower to do so. Remember "lost the keys to Halo 2 matchmaking" ? It sounded like even if Shishka wanted to update Halo 2 during Halo 3's run, Microsoft wasn't going to authorize the job existing, and Halo 2 was just stuck in the state it was in until original Live went down. I'm completely just guessing here, though.

Remember, Microsoft didn't even tell Bungie they were shutting down original Live ahead of time. They found out the same time we did that it was being shut down and that Microsoft had already pulled the DLC offline (which was thankfully restored again so people could participate in the final days). Doesn't matter if Bungie or 343 want to do something if MS doesn't allow it.