If they've got a system to detect it they'll ban them, sure, but as I don't think their banning system has changed since the good 'ol days of Halo 2 moding, cheating, and what-not, they'll do a mass ban on a friday at about 5:00PM EST.
You can't expect them to be able to accurately detect and then ban everyone hacking straight away, it takes time, and you can never expect them to catch everyone. Cheating is just something you'll have to live with in Halo 2, thats what you get with a community full of twelve year olds.